Repeat update notification

Afternoon all, just wondering if anyone could help on a quick problem - my Nexus 6 keeps prompting me to update but when I do it hangs after the reboot with what I assume is the recovery error message (red exclamation mark). I'm already on build LMY48I on 5.1.1, which I was under the impression was the September 2015 security patch. I'm fully stock, not rooted or any other mods. I am abroad currently, which I wouldn't imagine has any effect?

Could anyone offer any help on this or steer me in the right direction for further information.

Thanks in advance.