I'll answer in turn from top downwards.
> I tried saving using a different filename, in the same folder, in a different folder, etc etc. The link doesn't particularly help.
> I'd love to upgrade, but I cannot, as the software cannot find any updates. I assume it is because it is administrated by my organisation.
> My project is saved on the local drive. So that won't help unfortunately. I also tried saving on an external drive and that didn't work.