The type or namespace name ‘RSASignaturePadding’ does not exist in the namespace ‘System.Security.Cryptography’ (are you missing an assembly reference?) in Unit Test Project.

Was getting the below error while trying to build a unit test project (framework version 4.5.2) in VS 2012.

Delete the .messages file as suggested in some forums, but that didn’t help.

Just tried building the project by changing the Target Framework to 4.6.

That worked and after that on switching back the target version to 4.5.2 also worked.

Helpful post

https://social.msdn.microsoft.com/Forums/vstudio/en-US/2de45cd4-2744-4a91-91a2-785f305c1ef7/errors-on-trying-to-add-fakes-assembly-on-system?forum=vsunittest

Hope it helps..