Try to unlock again those gmapsupp.img with gimgunlock v.0.03+MapSigPatch
[Only registered and activated users can see links. ]
May be charts haven't been unlocked correctly for newer devices.
Drag&drop the .img in gimgunlock.exe, copy in SD/Garmin, one per SD, remove any other files from SD/Garmin.

Which firmware does 527 run?
It can be the latest firmware 4.00 got extra protection, but I doubt because it's not a new device.