Today Issue: We have a Citrix display issue with XenApp 4.5 for Windows 2003 when launching an application on 3 screens at 1280 x1024. The message displays: The following requested video mode was not available 3840 x 1024 x 16 BBP. Video mode restricted by system administrator.
RESOLUTION: If you have made changes to registry to increase memory on Windows 2003 with Citrix XenApp 4.5 then you have set SYSTEM permission to deny as per instructions on other Citrix/Blog sites.
Check permissions of this key \HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server\Wds\icawd\thin16 and allow SYSTEM.
Note: This does mean that if the farm settings are applied to the server propeties > Display any custom configuration will be lost. (see my other post on settings multi-monitor settings for 3 or more screens)
Information provided is based on issues I encountered and resolved, this solution may not be for everyone.
OS: Windows 2003 x64 R2
Citrix: XenApp 4.5