Yep, I went to test the drop down menu under "Receive Payment" and "Print Check" and couldn't select a customer nor a vendor. The week is already off a "great" ...
It would appear that I am having the same issue you are having with the drop down menu. Not only can I not select a product/service, I can not select the class ...
It looks like we were switched to the new invoice layout this week. So far, I much prefer the old layout. The new layout is not updating our recurring invoices ...