Can't access shared folders on NAS anymore ... "Volume expansion failed"

What firmware are you running?

Let's set aside the volume expansion warning for now.  The shares appear intact, and I think the first step is to regain access.  After that, I recommend backing up the files on the NAS. 

If you are using Windows 10, then it is likely that your access problem is because Microsoft is deprecating SMB 1.0/CIFS.  Try entering "run windows features on or off" in the the search bar, and bring up the control panel app.  Scroll down until you see the SMB 1.0/CIFS feature, and enable the SMB client if it is disabled.  You don't need to enable the server (though it is checked in the screenshot below). 

Note that SMB 1.0 isn't secure (and never has been) - that is why Microsoft is deprecating it.  However, your older NAS uses SMB 1.0/CIFS, not the newer SMB 3.0.  There are some options on this, but let's regain access first.

After the client is installed, reboot the PC and then try accessing the NAS again.  If that fails, post back - there are some other things to try.

On RAIDar, You could try running RAIDar 6.x - it can co-exist with RAIDar 4.3.8.  The download is here: https://kb.netgear.com/20684/ReadyNAS-Downloads#raidar