Talk to your domicile chief pilot's office and ALPA Mil Affairs. This happened to me last month and I found out that UAL/CAL recently merged portions of their pilot databases that feed into CASS and in the process some of us on long term mil leave dropped off a few key lists and thus out of CASS. You also need to make sure the company has a current copy of your license, medical and passport.
Prior to this SNAFU I have had no trouble jumpseating off-line.