Recently I installed TFS 2013.2 and modified some Build Templates. I also installed a separate Build Server that executes these builds for me.

My build template was based on the default TFS 2013 Build template (Tfvctemplate.12.xaml)

When my build executed, it ran for a while, but eventually it stopped with a nasty error message

An error occurred while copying diagnostic activity logs to the drop location. 
Details: Could not load file or assembly 'Microsoft.VisualStudio.Services.WebApi, 
Version=12.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one 

of its dependencies. 
The located assembly's manifest definition does not match the assembly reference. 
(Exception from HRESULT: 0x80131040)

The strangest thing was that my drop folder could be found and that the logs were there as well.

After searching for a while I found that it was all about 2 assemblies that were introduced in TFS 2013

• · Microsoft.VisualStudio.Services.Common.dll
• · Microsoft.VisualStudio.Services.WebApi.dll

I copied the assemblies to the Team Foundation Server Tools Directory (normally here: C:\Program Files\Microsoft Team Foundation Server 12.0\Tools )

I restarted the Team Foundation Server Build Service Host …

And my error was gone!

Hope this helps !