do you know about a program called sendmap20?

Please change the gmapsupp.img file with this new one
[Please Register or Login to download file]
If even after that don;t have any progress change the names and position of the two files so the gmapsupp.img to become gmapprom.img and on the memory device and the gmapprom.img gmapsupp.img and on the SD. After a research that i have done i realised that the problem apears because one map overlap the other and i had to split the hole map in two because it overpass the 2GB.
As it concerns your second question no it is not possible to transfer maps from the device on the Mapsource only if you find maps for PC.

I thank you for this next steps and I will test it out also But I did find a alternative to get USA or at least 49 states maps working.. as I dug a little more into this Garmin. I found that I could do it a little differently.

A. Connect the NUVI to pc with usb cable and backup up all folders of your NUVI drive to your pc

1. Download the US 49 states map from this forum new-maps-f88/city-navigator-north-america-2016-t16066.html
2. Then extract the gmapprom.img from it to the pc.
3. Then download sendmap20 pro and extract the zip file [Please Register or Login to download file]
4. Open sendmap20 program and drap and drop the gmapprom.img to the GUI screen
you will see the gui populate many map files
5. Select create gmapsupp.img button bottom right corner and store in same location on pc as the gmapprom.img
6. Then copy the gmapprom.img (1.771,601,920 bytes or 1.77GB )to the Nuvi drive in the Garmin Folder
7. Make directory on the 4GB SD card called Garmin
8. Then copy the gmapsupp.img to the SD card into the Garmin folder
9. Turn off the nuvi and insert the SD card into the NUVI
10. Turn on nuvi it boots up ,loads the map . you can confirm the map tapping the Wrench , then Map , map info

Note
11. This step is needed only if the gmapprom.img wont copy over to the Nuvi in step 6 On the NUVI go into each folder and delete any file that is not English like (Spanish, Dutch, British etc..) This free's up space.

As you like ! the map is the same and this program just copy the map on the device!
Please try the instructions that i gave you! Just to know the gmapprom.img is the first priority map and the gmapsupp.img on the SD the second one.

can you do this for Europe also
do I have to update the software from the gps?

The best and easiest way for a 660 is to download the Europe NT (not Unicode) PC install it on the PC unlock it and then Install on the device with Mapinstall the areas of the map that you need.
The 660 cannot recognize maps bigger tha 2GB so if you need all Europe you have to install an SD card also