Odd tho' it may seem, sometimes Citrix XenApp environments don't work that well. The reasons can be interestingly many and various and it may be required that you have to do some data gathering in order to better understand that its probably something to do with printing - or needs to be turned off and on again.

To help you help help your Citrix partner with this troubleshooting Citrix have released a tool matrix. The matrix  contains tools you should have running and in place to proactively gather data, and tools that you should have at hand and be familiar with should/when the time call. 

The list of tools applies to 

     * Presentation Server 4.0 for Microsoft Windows 2000
    * Presentation Server 4.0 for Microsoft Windows 2003
    * Presentation Server 4.0 x64 Edition
    * Presentation Server 4.5 for Windows Server 2003
    * Presentation Server 4.5 for Windows Server 2003 x64 Edition
    * XenApp 5.0 for Windows Server 2003 x64
    * XenApp 5.0 for Windows Server 2003 x86

For the list, see CTX122827 - Critical Tool Matrix for XenApp Environments

Also, don't forget about the wider and useful Tools of the Trade a more Microsoft Windows centric list of tools admins should have.