you get this error sometimes in presets. i have logged it at as a bug with rti.
TO DUPLICATE. use presets to add an item to the receipt, then close presets, and on the receipt make the quantity for that item 0. then try to go back into presets and you get this error.
WORK AROUND: delete the items from the receipt, do not make the quantity 0. if the employee does not have rights to do this, the manager will have to over-ride.