When running the QAS extensions for "Active Directory Users and Computers" (ADUC) on Windows under a forest with multiple sites it is possible to run into a problem when running ADUC from within a site that has no Global Catalog (GC). An error such as following can be found in the logs:
Unknown error 0x80131500
ERROR CODE: 80131500
Message: Global catalog not found in forest "xxx.yyy.zzz".
This problem can be tracked by defect ID #27814. This defect exists as of the Jan 2013 hotfix (184.108.40.206) but the fix is expected to be released in later hotfixes.