This behavior is caused by the same issue that causes the error "Error 55 Opening COM1". The problem is that the COM1 port has been opened by another application. Typically one of the following applications is accessing the port:
Microsoft Active Sync
Another GPS Software (i.e. Trimble Pathfinder Pocket)
Drivers such as those found with Folding Keyboards.
For information on how to troubleshoot GPS connections, see the Using ArcPad index, look for GPS - troubleshooting.