Verification Failed

Last night I was able to get iCloud Backup working on my iPad. At first it was failing but I bought more space from Apple and that allowed it to work - but it wasn't very clear that a lack of iCloud space was the problem.

Today I just got the following error message when I unlocked my iPad. I haven't changed anything at all except I am on a different Wi-Fi network than last night.

Verification Failed
The certifcate for this server is invalid. You might be connecting to a server that is pretending to be "setup.icloud.com" which could put your confidential information at risk.

Googling this error doesn't bring up anything relevant. Has anyone seen this before? Am I correct to assume that this is likely a temporary error?