Dont use IE7, it isnt supported and known to cuase issues.
Also, is this 2003 R2 by any chance?
Again not supported and we have had issues with this platform. Support for 2003R2 is introduced in September.
I have had two sites with this exact issue, the first one had default his internet security settings and that seemed to do the trick.
The other we had to wipe the machine and put the operating system back on and then all was ok again.
I have found 2003R2 to be problematic.
ACA - IP Office Implement
ACS - IP Office Implement
ACE - IP Office Implement