I tried replying by e-mail and it hasn't come through, so I'll reply using the web forums, and there may eventually be two replies with similar suggestions...
The second part of your issue got truncated, so you might want to include what else you said in a reply.
Regarding the gray thumbnails, this is usually a bad display profile, but can also be a corrupted previews cache.
dj_paige already posted a link to a page about changing the monitor profile to sRGB, although perhaps you’ve done that.
The other thing that could be wrong is your previews cache may be corrupted. The way to fix that is to delete the previews cache and let LR start a new one. If you don’t know where your catalog is, look in the LR Preferences / Catalog Settings and the path is indicated on one of the panels.
Using Explorer or Finder, go to the folder that has your catalog in it and your previews cache will be a folder called:
You should exit LR and then rename that folder to have a different name (using Explorer/Finder) and then restart LR. You could delete it, too, but if renaming doesn't fix the problem then you can just rename it back and have your old previews, again.
It is possible that there is some other problem that would be more obvious if we could read the rest of your message that was truncated.
Thanks ssprengel. Renaming the previews fixed the problem. I had already set the colour management to sRGB. The missing text in the question was that the backup fails and reports an error, presumably symptomatic of the same problem. Thanks again. I think I'll have a coffee now!