The OutputPath property is not set

This is driving me to the point of tears (metaphorically speaking lol)..

I'm using msbuild to build and deploy some web applications (.net 3.5+). What is odd is that i'm getting this error on shared projects but not in all solutions that use them. For example solution A includes shared project PaymentProviders.csproj and will build fine. However solution B includes the same shared project and i get an error...

"Error]  C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(483,  9): The OutputPath property is not set for project  'PaymentProviders.csproj'.  Please check to make sure that you have  specified a valid combination of Configuration and Platform for this  project.  Configuration='Prelive'  Platform='AnyCPU'.  You may be seeing  this message because you are trying to build a project without a  solution file, and have specified a non-default Configuration or  Platform that doesn't exist for this project."

Any ideas are appreciated.

Regards
Sean