InfoPath Dev

Hi, I'm having some serious challenges with something I thought should be standard SharePoint/InfoPath functionality... I've created a BCS model in a .Net Assembly with several entities; some of which have foreign key associations. When I create lists in SharePoint, it automatically provides an External Item Picker as part of the standard list form generated. At this point I can go in and create items, modify and view items... The problems starts when I try to modify the list from in InfoPath... even if I don't make any changes to the form, as long as I export to Infopath and then publish the list form back to Sharepoint, I consistently get the following error whenever I select an item from the External Item Picker or enter a value directly into it: "There has been an error while processing the form". This error persists as long as I try to select an item from the picker and the form never works properly again. If I edit the form in InfoPath and remove the External Item Picker, the form works just fine. It seems the form tries to submit prematurely whenever an external item is selected in the picker and then the error pops up! Has anyone come across this behavior before? I've searched the internet and tried reviewing the ULS logs but cannot find anything that points me to the problem and I'm frankly stomped!!! Any advise or suggestions would be much appreciated. Thanks