I recently upgraded from 11.04 to 11.10. I have several external hard drives, and now I cannot change anything on them: the permissions have seemingly been altered to read-only.

When I look at the "Properties" of each drive in Nautilus, it shows me as the owner, yet I can only "Access files". When I try to change this to Create and delete files, it shows an error message "Sorry, could not change the permissions of "124E43F04E43CAE5": Error setting permissions: Read-only file system".

I have tried to alter file permissions by starting Nautilus with "gksudo nautilus", but it doesn't work.
I have tried to change permissions for the whole drive using the chmod command in terminal. Still no success.

I am not a noob, but I am at a loss as to what to do next. Can anyone help? My back-up destination is one of the external drives, and I cannot back-up until this is fixed.

Thanks in advance.