Index: install/install_toolkit.php
===================================================================
--- install/install_toolkit.php	(revision 15165)
+++ install/install_toolkit.php	(working copy)
@@ -879,6 +879,7 @@
 		 */
 		function deleteCache($refresh_permissions = false)
 		{
+			$this->Application->HandleEvent(new kEvent('adm:OnResetMemcache')); // not in DB = 100% invalidate
 			$this->Application->HandleEvent(new kEvent('adm:OnResetConfigsCache'));
 			$this->Application->HandleEvent(new kEvent('adm:OnResetSections'));
 			$this->Application->HandleEvent(new kEvent('c:OnResetCMSMenuCache'));
Index: install/prerequisites.php
===================================================================
--- install/prerequisites.php	(revision 15165)
+++ install/prerequisites.php	(working copy)
@@ -38,6 +38,18 @@
 		protected $Conn = null;
 
 		/**
+		 * Version upgrade rules
+		 *
+		 * @var array
+		 * @access private
+		 */
+		private $upgradeRules = Array (
+			'5.0.0' => Array ('from' => '5.0.0-B1', 'to' => '5.1.0-B1'),
+			'5.1.0' => Array ('from' => '5.1.0-B1', 'to' => '5.2.0-B1'),
+			'5.2.0' => Array ('from' => '5.2.0-B1', 'to' => '5.3.0-B1'),
+		);
+
+		/**
 		 * Sets common instance of installator toolkit
 		 *
 		 * @param kInstallToolkit $instance
@@ -52,7 +64,7 @@
 		 *
 		 * @return kDBConnection
 		 */
-		function &getConnection()
+		function getConnection()
 		{
 			return $this->_toolkit->Conn;
 		}
@@ -68,26 +80,30 @@
 		{
 			$errors = Array ();
 
-			if ($mode == 'upgrade') {
+			if ( $mode == 'upgrade' ) {
 				$sql = 'SELECT Version
 						FROM ' . TABLE_PREFIX . 'Modules
 						WHERE Name = "In-Portal"';
+				$inportal_version = $this->getConnection()->GetOne($sql);
 
-				$conn =& $this->getConnection();
-				$inportal_version = $conn->GetOne($sql);
-
-				if ($inportal_version === false) {
-					// only, when In-Portal was installed
+				if ( $inportal_version === false ) {
+					// only, when In-Portal was installed (below 4.3.x)
 					return $errors;
 				}
 
-				$min_version = '4.3.1';
+				$min_version = '4.3.1'; // K4-based installator was created, that no longer maintained old upgrade scripts
 
-				$current_version = $this->_toolkit->ConvertModuleVersion($inportal_version);
-				$needed_version = $this->_toolkit->ConvertModuleVersion($min_version);
-				if ($current_version < $needed_version) {
-					$errors[] = 'Please upgrade "In-Portal" to version ' . $min_version;
+				if ( version_compare($inportal_version, $min_version, '<') ) {
+					$errors[] = 'Please upgrade "In-Portal" to version ' . $min_version . ' first';
 				}
+
+				// example: to upgrade to 5.1.0-B1 or more you at least need to have 5.0.0 installed
+				foreach ($this->upgradeRules as $min_version => $version_rules) {
+					if ( version_compare($versions[0], $version_rules['from'], '<') && version_compare($versions[1], $version_rules['to'], '>=') ) {
+						$errors[] = 'Please upgrade "In-Portal" to version ' . $min_version . ' first';
+						break;
+					}
+				}
 			}
 
 			return $errors;
@@ -166,7 +182,7 @@
 			$ret = Array();
 
 			$sql = 'SELECT VERSION()';
-			$conn =& $this->getConnection();
+			$conn = $this->getConnection();
 
 			$db_version = preg_replace('/[^\d.]/', '', $conn->GetOne($sql));
 			$ret['version'] = version_compare($db_version, '5.0', '>=');
Index: install/upgrades.php
===================================================================
--- install/upgrades.php	(revision 15165)
+++ install/upgrades.php	(working copy)
@@ -23,6 +23,41 @@
 	class CoreUpgrades extends kUpgradeHelper {
 
 		/**
+		 * Tables, that were renamed during 5.2.0 version upgrade
+		 *
+		 * @var Array
+		 * @access private
+		 */
+		private $renamedTables = Array (
+			'ban-rule' => Array ('from' => 'BanRules', 'to' => 'UserBanRules'),
+			'conf' => Array ('from' => 'ConfigurationValues', 'to' => 'SystemSettings'),
+			'c' => Array ('from' => 'Category', 'to' => 'Categories'),
+			'cf' => Array ('from' => 'CustomField', 'to' => 'CustomFields'),
+			'draft' => Array ('from' => 'Drafts', 'to' => 'FormSubmissionReplyDrafts'),
+			'emailevents' => Array ('from' => 'Events', 'to' => 'EmailEvents'),
+			'fav' => Array ('from' => 'Favorites', 'to' => 'UserFavorites'),
+			'img' => Array ('from' => 'Images', 'to' => 'CatalogImages'),
+			'#file' => Array ('from' => 'ItemFiles', 'to' => 'CatalogFiles'),
+			'rev' => Array ('from' => 'ItemReview', 'to' => 'CatalogReviews'),
+			'lang' => Array ('from' => 'Language', 'to' => 'Languages'),
+			'permission-type' => Array ('from' => 'PermissionConfig', 'to' => 'CategoryPermissionsConfig'),
+			'phrases' => Array ('from' => 'Phrase', 'to' => 'LanguageLabels'),
+			'g' => Array ('from' => 'PortalGroup', 'to' => 'UserGroups'),
+			'user-profile' => Array ('from' => 'PersistantSessionData', 'to' => 'UserPersistentSessionData'),
+			'u' => Array ('from' => 'PortalUser', 'to' => 'Users'),
+			'u-cdata' => Array ('from' => 'PortalUserCustomData', 'to' => 'UserCustomData'),
+			'search' => Array ('from' => 'RelatedSearches', 'to' => 'CategoryRelatedSearches'),
+			'rel' => Array ('from' => 'Relationship', 'to' => 'CatalogRelationships'),
+			'search-log' => Array ('from' => 'SearchLog', 'to' => 'SearchLogs'),
+			'skin' => Array ('from' => 'Skins', 'to' => 'AdminSkins'),
+			'submission-log' => Array ('from' => 'SubmissionLog', 'to' => 'FormSubmissionReplies'),
+			'theme' => Array ('from' => 'Theme', 'to' => 'Themes'),
+			'ug' => Array ('from' => 'UserGroup', 'to' => 'UserGroupRelations'),
+			'visits' => Array ('from' => 'Visits', 'to' => 'UserVisits'),
+			'session-log' => Array ('from' => 'SessionLogs', 'to' => 'UserSessionLogs'),
+		);
+
+		/**
 		 * Changes table structure, where multilingual fields of TEXT type are present
 		 *
 		 * @param string $mode when called mode {before, after)
@@ -1407,7 +1442,9 @@
 		 */
 		function Upgrade_5_1_0_B1($mode)
 		{
-			if ($mode == 'before') {
+			if ( $mode == 'before' ) {
+				$this->_renameTables('from');
+
 				// migrate email events
 				$table_structure = $this->Conn->Query('DESCRIBE ' . TABLE_PREFIX . 'Events', 'Field');
 
@@ -1537,6 +1574,23 @@
 		}
 
 		/**
+		 * Makes sure we rename tables to legacy names before doing other upgrades before 5.2.0-B1 upgrade
+		 *
+		 * @param string $name
+		 * @param Array $arguments
+		 */
+		public function __call($name, $arguments)
+		{
+			if ( substr($name, 0, 12) == 'Upgrade_5_1_' && $arguments[0] == 'before' ) {
+				$this->_renameTables('from');
+			}
+
+			if ( substr($name, 0, 13) == 'Upgrade_5_2_0' && $arguments[0] == 'before' ) {
+				$this->_renameTables('to');
+			}
+		}
+
+		/**
 		 * Move country/state translations from Phrase to CountryStates table
 		 *
 		 */
@@ -1681,7 +1735,11 @@
 		 */
 		function Upgrade_5_1_0($mode)
 		{
-			if ($mode == 'after') {
+			if ( $mode == 'before' ) {
+				$this->_renameTables('from');
+			}
+
+			if ( $mode == 'after' ) {
 				$base_url = $this->Application->BaseURL();
 
 				$sql = 'UPDATE ' . TABLE_PREFIX . 'FormSubmissions
@@ -1697,6 +1755,10 @@
 		 */
 		function Upgrade_5_1_1_B1($mode)
 		{
+			if ( $mode == 'before' ) {
+				$this->_renameTables('from');
+			}
+
 			if ($mode == 'after') {
 				$this->processDisplayToPublic();
 			}
@@ -1765,21 +1827,41 @@
 		 */
 		function Upgrade_5_1_3($mode)
 		{
-			if ($mode != 'after') {
-				return ;
+			if ( $mode == 'before' ) {
+				$this->_renameTables('from');
 			}
 
-			$this->moveTranslation('LA_COL_', 'LA_FLD_', 'ColumnTranslation');
+			if ( $mode == 'after' ) {
+				$this->moveTranslation('LA_COL_', 'LA_FLD_', 'ColumnTranslation');
+			}
 		}
 
 		/**
+		 * Makes sure table names match upgrade script
+		 *
+		 * @param string $key
+		 * @return void
+		 * @access private
+		 */
+		private function _renameTables($key)
+		{
+			foreach ($this->renamedTables as $prefix => $table_info) {
+				$this->Application->setUnitOption($prefix, 'TableName', TABLE_PREFIX . $table_info[$key]);
+			}
+		}
+
+		/**
 		 * Update to 5.2.0-B1; Transform list sortings storage
 		 *
 		 * @param string $mode when called mode {before, after)
 		 */
 		public function Upgrade_5_2_0_B1($mode)
 		{
-			if ($mode == 'after') {
+			if ( $mode == 'before' ) {
+				$this->_renameTables('to');
+			}
+
+			if ( $mode == 'after' ) {
 				$this->transformSortings();
 				$this->moveTranslation('LA_COL_', 'LA_FLD_', 'ColumnTranslation'); // because of "la_col_ItemPrefix" phrase
 				$this->moveTranslation('LA_HINT_', 'LA_FLD_', 'HintTranslation');
Index: units/helpers/user_helper.php
===================================================================
--- units/helpers/user_helper.php	(revision 15165)
+++ units/helpers/user_helper.php	(working copy)
@@ -363,6 +363,13 @@
 		 */
 		protected function _processInterfaceLanguage()
 		{
+			if ( defined('IS_INSTALL') && IS_INSTALL ) {
+				$this->event->SetRedirectParam('m_lang', 1); // data
+				$this->Application->Session->SetField('Language', 1); // interface
+
+				return;
+			}
+
 			$language_field = $this->Application->isAdmin ? 'AdminLanguage' : 'FrontLanguage';
 			$primary_language_field = $this->Application->isAdmin ? 'AdminInterfaceLang' : 'PrimaryLang';
 			$is_root = $this->Application->RecallVar('user_id') == USER_ROOT;