Lost contact with NAS after upgrading Windows 10

And also a message saying that an error occured during installation of add-on program prepR4ToR6

Installing the Prep add-on is not essential as if you have physical access to the device when the system comes up in a weird state you can then power down and do a factory default using the boot menu.

Is it now I should do a factory default using the boot menu?

First make sure you've backed up your data and verified it if you haven't already.

Install the R4toR6 firmware image, accept the prompt to reboot now.

The system should reboot itself a few times or so and come up in a weird state (OS6 installed over the top of RAIDiator-x86). The system won't be working in this broken state.

At that point you could power down and do a factory default (wipes all data, settings, everything) using the boot menu.

Alternatively (or if the above doesn't work for you) you could do a factory default (System > Update > Factory Default), and after it comes back up try installing the Prep Add-on Again, Install R4toR6 firmware image, and accept the prompt to reboot and the system will automatically trigger a factory reset at the appropriate time.

Note that if you do a factory default whilst still on RAIDiator-x86 4.2.x you could open RAIDar to select the RAID mode and confirm your choice to avoid having to wait for the 10 minute countdown to complete.

It appears the old User ID and password does not work any longer. Any suggestions?

Factory default will have set your login to User: admin & Password: password

It may have also (re)set your Lan settings to DHCP and switched off quotas

Use Raidar (DOWNLOAD) to discover your NAS on your network for a better idea of the current state of play

As far as I can tell from the progress so far, the NAS appears to be up and running OS 6.9.4. Further testing will tell. A user manual for 6.9.4 would help. Does anyone know if there is such a manual, and if so, where to find it?

Might there even be a manual available in Swedish?

Look HERE

Excellent, now I have a manual. When trying to configure backup on one of my computer i get an error message: "Reconnect the unit"

:

How do I reconnect the unit? 

Can you simply access the NAS shares from file explorer?  This is to confirm setup.

After that, I suggest looking through the backup faq for your particular use case: https://kb.netgear.com/29788/ReadyNAS-Backup-FAQ

Yes, I can access the NAS shares from file explorer, so it appears the setup is ok.

I have finished the first 50 pages of the software manual. I will finish the rest and look through the backup faq to see if I can find out why backup does not work.