Starting In-Portal 5.0.1 (possibly even 5.0) we have came across the
situation when Cookie hasn't been set due to issue with script sending
extra output (wasn't buffered by PHP) during it's runtime. This lead
to the issue with properly setting the Cookie when required. In
particular this happens on the Front end when you are trying to add a
product to your cart and new session is created, but can affect other
places as well.
The above issue is ONLY in affect when PHP configuration setting
"output_buffering" has NO value. By default it's set to 4096 (4K), but
sometime changed to No Value.
Here is a link to PHP manual with more description on Output Control
system in PHP http://www.php.net/manual/en/intro.outcontrol.php
While it was done before - the task is:
1. check and find all places where extra (early) output is sent.
2. Do check before installation on "output_buffering" setting which is
preferable to have some value.