if you add product and quantity 2 and go to pay for it by returning to the site you see this message

Query:
INSERT `sys_acl_levels_members` (IDMember, IDLevel, DateStarts, DateExpires, TransactionID) VALUES (2, 4, FROM_UNIXTIME(1256392438), FROM_UNIXTIME(1257256438), 'KGTB0717HFH47Y99')
Mysql error:
Duplicate entry '2-4-2009-10-24 15:53:58' for key 1