Driver corruption or job corruption.
Since it applies to a user, it will either be a driver,workflow or application thing. It can't be the printer since it is assumed nobody else has an issue. So if the same file, printed from the same application, on the same PC, using the same PIN works once and not the next, it isn't a setting (that would apply to both) it would have to be corruption.
And the only answer there is to completely remove the driver and port installed on that users client, then install the latest driver, with a new port, make it LPR and make sure LPR byte counting and SNMP are both disabled.
I have a user who is reporting their secure print pin will work on some print jobs and not others. I have confirmed he is using the same pin each time and other jobs will release without any issue. Any ideas as to what would be causing this?