When I try to post a batch, I get an error “Error posting venture cost batch: Could not add bill to QB. There is an invalid reference to QB account “

This is caused when there is a cost type setup in VISCO that is not in QB so one or more of the vouchers in the batch did not post to QB. You need to setup the cost type in QB and post the voucher(s) again. Check which vouchers posted to QB before posting the batch again, otherwise you may have duplicate entries in QB