Ran into an issue today on a Windows 2003 Citrix farm. As soon as about 30 users logged into a server, any user thereafter received the following error:
Windows cannot load the user’s profile but has logged you on with the default profile for the system.
Detail: Insufficient system resources exist to complete the requested service.
Event IDs 1505 and 1508 errors appeared in the application log.
The server had plenty of memory left, so it wasn’t actually that the server ran out of RAM. It was just an issue with how Windows was allocating it. After some research, I found this article:
Tim Rettig's Blog 