"The located assembly's manifest definition does not match the assembly reference" error after installing AjaxControlToolkit via NuGet

Question

The full error:

Parser Error Message: Could not load file or assembly 'AjaxControlToolkit, Version=4.1.7.1005, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

This doesn't make sense because the package version I installed was 4.1.7.1213. When I look at the build server logs Nowhere do I see any other version than that.