I suspect I damaged my MD 25 by running it with the jumpers set improperly. I didn't even look at the jumpers until about a week ago. Up until that time, for about a month, I had been running the Serial as well as the I2C with both jumpers on (the configuration as it was shipped from the factory). This may be the reason why my program is stopping at the first call to the MD25. When I first started running the Serial with both jumpers on, the motors were turning and the LCD was displaying values to V and encoder, etc. Performance degraded after the first few runs of the program, however. Anyone have similar problems? Were your problems solved by using a new MD25?