Some of the first NexStar 11 GPS scopes to reach owners have an older version of motor control board which does not allow the owner to upgrade the firmware and is not compatible with the newer version of hand control (version 4.03 and higher). Read here to determine the version of your motor control firmware. If your motor control is version 3 or higher, you can download firmware and install from your PC as described here. If you determine you have version 1 or 2, you should get a replacement motor control board.
Celestron did sells the newer motor control board for about $150 (price may change) in the past - contact them via telephone or via the support section of their web site (www.celestron.com).
If you do manage to get a newer motor control board, you will need to remove and reinstall the board. Click here for the instructions for removing and reinstalling the motor control board - thanks to Jim Towers for scanning this document. Also, here is a newer version of the instructions that Celestron is currently using - I would recommend reviewing both the older instructions and these newer instructions prior to replacing the board.