This can happen on Terminal Server/Citrix servers under heavy load because pool memory is a finite resource and by default is tuned to the middle setting. This may manifest itself in user’s PKG files being written out as 0KB files and causing launch failures the next time the app is used. It can also cause 2020 or 2019 errors in the event log and cause the server service to fail to allocate resources which can also cause the Terminal Server computer to refuse connections.
In a Microsoft Exchange world, this setting needs to favor PTEs but in TS we use very few PTEs and thus can tune the other way to maximize pool memory. See http://support.microsoft.com/kb/312362/en-us for more information on the error and how to tune this setting.
Microsoft, SoftGrid, Microsoft Application Virtualization, Terminal Server, Troubleshooting