Error while compiling / debugging VB 2008 source code

I am working on a VB programm in Visual Studio 2008. It worked fine, but from one day to another I got below error message. I can not manage to get rid of it. Is there anyone who can help. At this point my program cannot be build or compiled nor tested.

Unable to read manifest 'My Project\app.manifest'. Could not load file or assembly 'System.Data.SqlXml, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' or one of its dependencies.

The manifest file is in the correct place. I did download system.data.sqlxml and placed in also in the bin. but no res开发者_Python百科ult. I do not know what i did that made this error. It just was there at once. before all worked fine.

Please help ! Thanks