I'm running out of ideas now. It may be as i suspected earlier that this mysterious V1.6 is some early experimental fw which is incomplete, deep Alpha rather than just Beta or UAT. As the device attains preboot mode and Updater.exe sees it at first it's quite odd that the flash is properly initiated (indicated by "Loader" on screen) yet then the flash always stalls and Updater consistently times-out. I guess you've been persistent with flashing attempts with Updater, some devices can be stubborn. I see you tried a couple of different OSs, 7 and 10. Have you tried on totally different PCs, directly using rear desktop USB2 ports only (no USB3 ports or hubs) and also using several different usb cables? Clearly you have Garmin USB drivers loaded or updater wouldn't even see the device.

As for other methods of flashing/updating firmware or other programs, you've tried them all i think. Here are the possibilities anyway, device dependent. Somethings should work for sure but perhaps not all however even in a healthy device:

  • Connect to GarminExpress or WebUpdater conventionally to get update from Garmin server
  • Drag GCD onto WU icon on desktop or directly onto WebUpdater.exe
  • Place GUPDATE.GCD in Garmin folder on SD and boot
  • Place GUPDATE.GCD into device's (hidden) .System folder and boot (i think E20 has .System, if not GCD into device's Garmin folder)
  • Flash RGN file by Updater.exe in preboot
  • Flash 14.bin via SD card commands with Ldr.bin

I can't think of any others at the moment.