(Whomever you are),
I have no experience with JMRI's RFID features, but I would guess that you have an Olimex reader and RFID "tags" which are not supported by JMRI.
It is my read of the source code and Olimex user manuals that JMRI supports the Olimex MOD-RFID1356 reader and associated tags.
It is my guess that you have the Olimex MOD-RFID125 reader and associated tags. JMRI does not appear to support that reader and its tags. That reader returns only 40 bits of tag id data.
JMRI's Olimex support expects to receive 64 bits of tag data, as reported by the Olimex MOD-RFID1356 reader.
Regards,
Billybob
