I am having exactly the same issue.  I am also connecting to a Oracle backend.

There is no stack trace.  Just a Visual Studio standard error dialog box with the error message.  Is there something I can do on my end to help figure this out?  I definitely want to get rolling with the WBBS. 

Does the error give you any sort of stack trace?  I don't think any of the design-time stuff should be trying to access the database.

I have a page with a WWBS control.  When I click on the BusinessObjectName dropdown in the designer, I get the following error:

"Unable to cast object of type 'System.Data.SqlClient.SqlConnection' to type 'System.Data.OracleClient.OracleConnection'"

Does anyone know what might be causing this and how I can get around it?

BTW, I am using an Oracle database.

Cheers!