I've had problems erasing/writing to flash a few times. This was while
using motorola MCUs.

1. Is the power supply on the PCB that is failing able to supply the
voltage to erase the flash? I've had problems erasing it coz the power
supply i was using was current limited. Of course this would not happen
on a PCB that has worked before unless the power supply got busted in
some way.

2. Sometimes the problems lie in the tools or the communication lines.
Test your connectors, restart your hardware tools, restart your PC to
reset the drivers.

I don't have any TI specific advice to give you coz i've only just
started using one.

-- Arya