NUnit is now at Version 2.5.10.
The Nuget Package constaints the dependencies of NUnit to NUnit (≥ 126.96.36.19913 && < 188.8.131.52)
So when I have NuGetted NUnit at 2.5.10, then NuGet FsUnit I get NUnit 184.108.40.20648 loaded too.
FsUnit source code compiles and all tests passed with NUnit 2.5.10
Please find time to update the NuGet packages.
Thanks for your efforts on FsUnit - I'm getting great benefit from using it.