Problem upgrading ReadyNAS Ultra 4 to OS 6

Thanks for your response, Sandshark!

Following your suggestion and the instructions in the link provided, starting usbrecovery.exe on a Windows 10 PC resulted in an error message that said in part "The application has failed to start because its side-by-side configuration is incorrect." Checking Windows' Event Viewer led me to install "Microsoft Visual C++ 2005 SP1 Redistributable Package", which fixed that problem.

Used a 1-GB USB drive and created the recovery USB. It was noticed that usbrecovery.exe would not "see" R4toR6_6.9.5.bin even when it was the only BIN file in the directory. Renamed R4toR6_6.9.5.bin to RAIDiator-x86-R4toR6_6.9.bin then it appeared and was selected. Usbrecover.exe reported "Not responding" for a few seconds during the process, but then later said "Done".

Followed the instructions from the link you provided, but after holding the Backup button for 15 seconds (by a watch) the device started its normal boot process. Tried longer times in five-second increments, same results until I held the Backup button for 30 seconds. Never saw anything on the LCD that said anything about USB Recovery mode, just the far left block in the upper row blinking on and off.

But then a bit over 60 seconds after releasing the Backup button the device powered down, just as predicted in the instructions! (The instructions did not suggest a time to power down.)

Removed the USB drive and tried booting normally, but no joy, it still stalls out at 80-plus percent and showing "quotarpc.service" on the display.

Downloaded R4toR6_6.9.5.bin again from the same link as before and re-created the recovery USB, same results.

Now what?