Ordinarily I'd say that it could be a failure to pay, chargeback on the registration, false information supplied etc. That would be a little on the late side since the original registration was in 1996 though....
OTOH there may have been a dispute involving the name, the expiry date could be listed incorrectly (gasp), or <insert plausible reason here>.
Hopefully PIR will eventually give some indication of how long they're going to keep .org names in PENDING DELETE status.
Best wishes,
Simon.