Hi Marvin. I apologize that it took two months to get your Book Port repaired. That is not the norm, and we are working to decrease the time that any unit must be out of its owner's posession. Unfortunately, we do not know that the DEF command was actually the problem. This would most likely have happened even if you hadn't used the command. What probably happened is that the battery contacts were slightly bent and as the unit was booting up after the battery change, the batteries lost contact for a brief time. >>> mjslipp@xxxxxxxxxxxxxx Thursday, December 15, 2005 1:33:29 AM >>> This is Marvin Kotler. I had a book port for 16 months. In all that time, I used the d e f command without difficulties. Then one time when the batteries were low, I used this command again and the book port went south. I had to send it in for repair and it took two months to get it back. I was told to use the d e f command at my own risk. So, who knows what happened. It is now working again properly; everyone have a happy holidays.