Hi all,
I understand that this is not the proper forum for unit specific discussion but this pertains to Basecamp and BirdsEye as well as the Montana 650T. I am unable to find a Garmin forum for specific units and would have paid money to know this little bit of info a few weeks ago!
Montana 650T can have ONLY 249 .jnx files (BirdsEye images) on a micro sd card. If you have 250 or more on the card the unit will not turn on. It does not appear to be a matter of how large those 249 files are. If you have more than 249, you must remove the card from the device, remove the required number of files through a card reader, and then it can be put back into the unit.