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There could be one or more of many possible issues involved. It could be the naming and/or placement of the individual map files although MapInstall should attend to that properly. It could more likely be that the PC installed mapping data (.gmap folder) is unlocked solely for use on your computer rather than also unlocked for your particular device, or not locked at all in the case of you being able to see some maps. It was even common for old Garmin maps to be made without implementation of any locking provision at all because some very early Garmin GPS devices didn't even support locked maps used with a 25 numeral unlock key (i.e. "MAP" protection), never-mind the current GMA/MSV protection as additionally used in your Alpha 100.
Have a read of some [Only registered and activated users can see links. ] to see if you can clarify your particular issues and build your knowledge and understanding of the core problem. Then if you need further assistance come back and post here with detailed info and even screenshot examples of files/folder naming and layout of the problem if required.
There's no such thing as "too much info" when we're trying to remotely troubleshoot an issue .
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