Thanks Robhogg - that worked! It took a while to run the check for bad blocks, but it did work. Only thing is I then got a different error message:
You don't appear to have enough disk space to install the packages you've selected. You need more space on the following file systems:
Mount Point Space Needed
I have no idea how to increase the space of the mount point /. I installed this a few years ago and I think just did the default set-up. I use this system for one purpose only, and that is to serve my FLAC audio files to my Slim Devices (now Logitech) Squeezeboxes using Slim Server (which is now called something else too I think). ClarkConnect was recommended for that as it had Slim Server built in as a service. It worked very well until quite recently, when I had to put in a new NIC. Since I had the thing pulled out, it made sense to see about upgrading. I was going to upgrade from 3 to 4 and then from 4 to 5 (3 to 5 isn't possible).
I have all my FLAC files backed up, so would it make more sense simply to start again with a fresh install of version 5? Or is there something more suitable and user friendly now? If it's straightforward enough to increase the partition size for the mountpoint mentioned, I'd be up for trying it.
This is a screenshot of my partitions and drives:
Does that make sense?
Thanks so much for the help so far folks. You rock!