I have installed Tortoise CVS 1.12.5 on a windows 2008 R2 SP1 server and the context menus do not display.
Checking the Event log reveals a Windows Side by Side error. The error is
Activation context generation failed for "C:\Program Files\TortoiseCVS\TortoiseShell64.dll". Dependent Assembly Microsoft.VC90.CRT,processorArchitecture="amd64",publicKeyToken="1fc8b3b9a1e18e3b",type="win32",version="9.0.21022.8" could not be found. Please use sxstrace.exe for detailed diagnosis.
Tortoise CVS 1.12.5
Windows Server 2008 R2 SP1 64 Bit
I had the same issue, solved by installing Microsoft Visual C++ 2008 SP1 Redistributable Package
http://www.microsoft.com/download/en/details.aspx?id=5582 (32 bit)
http://www.microsoft.com/download/en/details.aspx?id=2092 (64 bit)