My Dakota 20 would not power up today. I tried suggestions made earlier. No joy. I deleted the gmapsupp.img file. Device powered up. I updated my device last night to the latest version of of the firmware. The gmapsupp.img file was made prior to the update. After deleting the img file I opened MapInstall. It too had an updated. I updated the MapInstall application and then reloaded the supplimental maps to my device (i.e. created a new gmapsupp.img file). Everything apears to be working. Hope this helps.
BTW, a few other items i came across while researching this problem (I'm new to the forum and these may be well know - appologies if i'm going over old ground).
1) GarminDevice.xml apears to be created every time device powers up. Before I hit on the process described above I opened this file. It appeared to be incomplete - the xml tags didn't lineup. I deleted it but it came back after next power up attempt.
2) Open the Satelite screen and press down in the upper left courner of screen. After a few moments you'll enter the diagnostic screen. I found this in an Origon discussion. Apparently it works on the D20.
3) The process for a hard reset on the Origon gps is to press on the upper left courner of the screen while powering up. After a while you'll be prompted to reset. I tried this on the Dakota 20 with no luck.