Unhandled Exception. We Hate Them, But They Happen

I am creating speech recognition software using AT&T's api located here: http://developer.att.com/sdks-plugins/att-sdk-for-unity. It gives a .dll file as usual. Now the software works fine in the editor, but when trying to build/run in any platform, I get the error message;

Internal compiler error. See the console log for more information. output was: Unhandled Exception: System.TypeLoadException: Could not load type 'System.Runtime.Versioning.TargetFrameworkAttribute' from assembly 'ATT_MSSDK'. at Mono.CSharp.Driver.Compile () [0x00000] in :0 at Mono.CSharp.Driver.Main (System.String[] args) [0x00000] in :0

Does anybody have any experience with this problem?

Thanks in advanced!