Comment 1 for bug 1248639

This is odd. Note that the log file likely contains more information, although I don't know how helpful that would have been either. I'll bet you'll see

No valid image master key found

in the log file. The messages just before this would shed more light on the actual problem.

What this is saying is that the client tried to go out to the server to find an image-master.tar.xz keyring file, but there was some problem in downloading that file. Either it didn't exist on the server, or the json data didn't match (the model or type was wrong, or there was an expiry key containing a past timestamp), or the actual signature on the .tar.xz didn't match the associated .tar.xz.asc file.

In all likelihood this was a problem on the server which subsequently got repaired. The client will self-correct.

I can see where the exception is misleading. Probably it's better to re-raise the original exception, though it's always going to be the case that the log file will contain more useful details.