Why can't I re-enable iCloud Keychain on my iMac?

Hi,

I recently noticed that iCloud Keychain stopped syncing passwords between my devices. While my iMac was up-to-date, my iPad mini, iPhone and MacBook weren't. I found a support article that suggested disabling iCloud Keychain on all devices and re-enabling it later. I followed that advice only to be presented with a completely new issue.

On my iMac (27" Late 2012, Mac OS X 10.9.1), when I try re-enabling iCloud Keychain, I get the following error message after waiting for a few minutes:

"iCloud Keychain couldn't be set up because there was a problem communicating with iCloud. Try turning on Keychain again." (transcribed for sight-impaired users and search engines)

I've tried this about a dozen times over the past few weeks now (just in case it is a server-side error), but still no luck. I tried investigating and found the following error message pop up in Console at the same time as the error in the above image:

13.02.14 16:44:59,761 com.apple.preferences.icloud.remoteservice[9342]: [AOSAccounts] : [registerCredentials] : SOSCCSetUserCredentials Error The operation couldn’t be completed. Invalid argument.

Does anybody have any suggestions on what I could try to overcome this issue? Or could anyone from Apple see if there is something wrong with the iCloud Keychain data in my account?

Any kind of help is greatly appreciated.

Cheers,

Alex