Can no longer access NAS on clean install of 20.04

Solution 1:

One way to resolve this issue in Samba:

Edit /etc/samba/smb.conf

That file will be added when you install either the samba package or the smbclient package. If you don't want to install samba install smbclient:

sudo apt install smbclient

Then edit /etc/samba/smb.conf and right under the workgroup = WORKGROUP line add this one:

client min protocol = NT1

Another way - and one I prefer myself - is a cifs mount.

Solution 2:

I added these two lines to smb.conf in the [global] section and that fixed it for me on Xubuntu 20.04.

client min protocol = NT1 

server min protocol = NT1

More details are given here: Broken samba shares