I ran into this problem last week.

Here’s the solution:

To install this, please follow the steps below;

Unlock code: They gave the unlock code.

Windows computer:

1) Right click your mouse on the desktop of your computer, then select “New“, then select “Text Document“. This will place a new text document icon on your desktop
2) Double click on the newly created Text Document icon on the desktop to open the text document window
3) Copy the above unlock code into the document.
4) Click “File”, then “Save as”
5) In the “Save as” dialogue box, change the file name to gmapprom.unl 
6) Change the “Save as type” to “All files“, then save the document and close it
7) You should see the file “gmapprom.unl” on your desktop as an icon
8 ) Right click on the gmapprom.unl file on the desktop and then select “copy”
9) Plug your Garmin device into your computer and then open “My Computer” or “Computer” This will show the devices attached to the computer
10) Double click on the Garmin or Nuvi drive to access the files on the GPS.
11) Right click on the Garmin folder and then select “paste” to past the gmapprom.unl file into the Garmin file folder.
12) Safely disconnect your Garmin device from the computer electronically before disconnecting the cable.
13) Disconnect the USB cable, then power the GPS on…..

Any questions? Drop me a mail.