After some further testing I discovered this error is caused by a version bug between .Net4 and .Net4.5 assemblies. The single DLLs were built on a windows 8 machine which turns out was secretly using .Net4.5 assemblies, which then breaks if run on a machine which only has .net4. A quick fix is to use either the .net3.5 or .net2.0 build or install .net4.5 but in the long run we will find a way of ensuring this workaround is not necessary.