getting exception after upgraded to .net framework 4

Hi,

I’m using Visual Studio with Crystal Reports 9 to create a Windows Form.  I’ve changed the “Target Framework” of my project from 3.5 to 4.0.  After that, I’ve started to receive an exception when I try to run my report. The exception says:

“Could not load file or assembly 'file:///C:\Program Files (x86)\SAP BusinessObjects\Crystal Reports for .NET Framework 4.0\Common\SAP BusinessObjects Enterprise XI 4.0\win32_x86\dotnet1\crdb_adoplus.dll' or one of its dependencies. The system cannot find the file specified.”

The strange thing is that this does not happen ALL the time.  It usually gives that exception, but ones in a while the report runs fine.  What is causing that?

Thanks so much.

Aron