One of our VMC4020 mill (88HS control, DC) has developed something odd.

We can upload programs to it but not save them to memory. Existing programs in memory can be called up and run with no problem. New programs can be uploaded and will also run with no problem but they don't show up in the program list. We receive a "CANNOT FIND PROGRAM" error message when trying to load a new program from memory.
We use BobCAD and Predator to program, uploading and saving works fine on our other 4020.

We have deleted a whole bunch of old programs, pulled and re-seated all cards and relays, to no effect.

Has anyone run into something like this before and if so, how did you remedy this?