php can not clean up

[william drescher]

occasionally when I use an application I am developing I get the
following error:
Notice: session_start() [function.session-start]:
ps_files_cleanup_dir: opendir(/var/lib/php5) failed: Permission
denied (13) in /var/www/MP2010-v2/challenge.php on line 2

This started when I upgraded Ubuntu from relase 9.10 to 10.04.

my directory has the following permissions
drwx-wx-wt 2 root root 4096 2010-10-12 07:19 php5

First question: what is wrong and how do I fix it.

I suspect that the owner or group of this directory should be 
apache.  What user does apache run as ?

bill