The PLC EEPROM is probably corrupted. Try going to TLServer and open up the Serial Port Setup, then check the PLC ID by typing:
IR*
If it responds IR01* the ID is still 01 or it could be something else. Anyway, you can then clear the PLC transfer protection password using the following:
@01$cKILL00*
(01 is the ID, replace with whatever new ID or change the ID to 01 first before using the above command).
The program will also be cleared (which shouldn't matter to you since it is corrupted anyway) and after that you should be able to transfer program to the PLC as usual.
If it doesn't work or same password request still shows up after trying the above command, then the EEPROM may be damaged and need replacement. You can contact sales@tri-plc.com to purchase replacement part.