already Existing my project run in VS2003 but not run in VS2008 , this
error is comes
Microsoft SDK setting "c:\program files\microsoft sdks\windows\v6.0a
\include"
It seems that you or someone or something else tampered with the oledb.h header file and now it has errors.
The best you can do is uninstall, make sure C:\Program files\microsoft.... etc. is deleted before reinstalling VS2008.
Also note that if instead of doing that, you can install the new SDK for Windows 7 if it is publicly available, and configure VS2008 to use the new SDK. I have it because I saw it in MSDN Subscriber downloads, so I'm not sure if this one is out for the public or not.