Solved

An error while importing .reg files in the registry:
http://www.codeguru.com/forum/showthread.php?t=351113
The solution was to save the as US-ASCII in VS.

Deleting files older than X days:
forfiles /p [DirectoryPath] /s /m *.* /d -X /c "cmd /c del @file : date >= X days"
http://technet2.microsoft.com/windowsserver/en/library/9660fea1-65c7-48cf-b466-204ba159381e1033.mspx?mfr=true

If VSTS test passes when run as "Debug" but fails mysteriously when just "Run" and test accessors are used, it is time to refresh test accessors. The best by deleting them and regenerating.