My TB177b HMI won't connect to the plc (PLC 317-2DP). It connects through ethernet to the ethernet module on the rack (CP-343-1). I can ping the device just fine, and download my project onto it, but when runtime boots up I get an error "PLC Diagnostics not possible error code:8000104".

Whats even stranger was I just had this working with another TB177b just yesterday on the exact same setup and it was communicating just fine with the plc. I tryed downloading the project to a new TB177b HMI today and everything downloaded fine but no connection to the PLC. The old screen that was working yesterday also stopped connecting to the PLC.

There's no hardware faults on the Ethernet module or the PLC, can anyone think of what might be wrong? Im stumped