I am running Visual Studio 2010. I just change the frame work of my project from 4.0 to 3.5. I removed the reference Microsoft.Framework that it asked me to remove then trie
You can try regenerating the file by right-clicking the .resx file and choosing 'Run Custom Tool' from the context menu.
Edit: before you do this, change the Access Modifier or add a new value to force a regeneration.
Another edit: See Downgrade an application from .net 4.0 to 3.5 for another possibility