I've not had this issue at all - I print mine in bulk through selling manager, and only print the Invoice / packing slip option, but I just tested it with a single order and that also loaded up fine.

Glitches can affect different accounts at different stages occasionally, though - have you been switched over to managed payments or received any notice about it? eBay make changes to accounts to prepare for the switch and this may sometimes cause some temporary technical difficulties, I think.