OCS 2007 R2 Bug
There is a known bug in OCS 2007 R2 (and I presume 2007) whilst using the Remote Screen feature.
If you try to run an elevated process under Vista/Windows 7 and have UAC enabled the Accept box for UAC (the Yes/No prompt) is ran in the “Secure Desktop” and therefore inaccessible to the user.
This is also the case if it prompts for a username/password.
From what I can see the only way around this is to DISABLE UAC – not recommended obviously.