Further analysis:
a) I was connecting remotely using vnc4server.
b) Connecting locally allows me to mount any of the"problem" discs OK.
c) If I mount the disk locally and then access the server through vnc4server I can open and access the disk.
Thus the problem seems to be related to use of vnc4server and possibly permission settings that got changed on upgrade ?
Further analysis:
a) I was connecting remotely using vnc4server.
b) Connecting locally allows me to mount any of the"problem" discs OK.
c) If I mount the disk locally and then access the server through vnc4server I can open and access the disk.
Thus the problem seems to be related to use of vnc4server and possibly permission settings that got changed on upgrade ?