Could be that your baud rate is not close enough.

Could be that you have marginal RS232 voltage levels.

Could be you have an intermittant connection in the cable or RS232 circuit on the microcontroller board.

Could be a circuit got shorted to another in the process moving the elecronics.

Could be a ground problem...

Simply put it could be most anything. You will want to get your hands on an oscilloscope so you can look through the circuit and see which part is marginal.

Michael Karas