Issues creating expense report

When entering a list of expenses in the create expense / receipt window I am experiencing an intermittent error message. Clearbooks will not allow me to confirm the expense report and gives me this error message:

Account: Please do not leave empty

despite the dropdown for bank account and payment method being complete, this has occurred a couple of times on detailed reports with a number of line items. never seems to occur on simpler reports with one or two line items.

I can't get round it and have lost quite a lot of data entry time