krispy67
there are some files error in your Nuvi the next suggestion is hard to do so you can try but it up to you.
In my experience I backup all files in Nuvi drive(fw 4.90us) then format it and let the Nuvi to restart it will create folder .System,garmin and gpx.
don't worry it not brick you Nuvi, conect Nuvi to PC and update firmware by webupdater to fw.4.90us again and follow the instruction in program
install everything in addtional update, disconect it the Nuvi will reboot and create a folder increase in garmin drive.
Copy your backup files to new Nuvi drive and don't replace the files that Nuvi create by itself let it reboot and look up in inventory screen
Boot BLK,X-Loader,System is 4.90 I think it can solve your problem if you don't want to format your drive you can try rename .System folder
and do as above.
Then doing follow the quick guide to convert to Nuvi 1490 3.00TH
Good Luck