This is a standard problem with
Maxsea, caused by its ability to interface with lots of different systems, and the default setting being one that is not compatible with the normal output from a gps mouse.
The method of resolving will depend on the
maxsea variant that you have.
However, there is another idiot check first - the GPS will only
work with one system at a time, unless you have something like franson gpsgate. I spent hours trying to chase what was happening on mine, when I could see it happily on a utility that checked the output, but could not find it on Maxsea, before realising that of course the utlity had captured the GPS comm port, and maxsea could not possibly use that comm port at the same time.
Thus assuming maxsea is set up to look at the correct comm port, and nothing else has captured the comm port first. The problem is almost certainly that maxsea needs to be reset to accept the correct
nmea sentence that is being sent by the mouse. Maxsea does (or at least my version does) have a folder where you can see what is being received from the gps source. Unfortunately, there are a number of different messages that
NMEA uses to transmit the position etc. and looking at what is being actually received will enable you to set the system so that it is looking for that message for the data. The handbook should give you more info on this, as I am having to be somewhat generic, not knowing anything other than version 10.1 and 10.3