User cannot run C# released app - "The application failed to init.properly"

I am desperate due to this problem: I have created and built app which works fine on mine and my colleagues PC. However, third user reports that with .NET 3.5 the app reports: "The app开发者_高级运维lication failed to init.properly" and with .NET 4.0 "Unable to find the version of runtime to run this application“. Could you please advice? It was built with 3.5.

EDIT:After installing 3.5 SP2, there is no error message. It just does not execute :(

Thanks

For .NET 4.0 version problem is that the framework is not installed on the users PC. For .NET 3.5 if you are sure that the needed version of framework installed then most probably user doesn't have access to some system file required by the application.