In one of my projects I am trying to set Data Source Settings on combo boxes.  On all of them I have tried it comes up and then the settings form disappears and I see the wait window saying it is looking for business objects.  This just stays up and I never get to the population data source settings.  I end up having to exit the project and can't get the settings to come up.  This is the only project I have seen it happen in, but it happens on all of the combo boxes.

If you comment that one business object out does the error persist?  As for the error messages getting snuffed, this is thanks to Visual Studio.  It is actually very hard to show an error in the DTE....you have to put a try catch around the exact location that is failing...even then it is a crap shoot.

How do you know you have it narrowed down to a single BO?  If this is the case, post the BO source code so we can look at it and see if there is something fishy.