verification failure query

hi everyone.

am wondering if you can help

I've had a message intermittently over the last few days and wondering what I can do to get rid of it, if at all

when in settings, I've clicked on icloud and get 'Verification Failure - unable to connect to icloud'

I've rebooted by holding home and sleep buttons for 10-15 seconds and also reset network settings.

is there a generic problem, or just me? it doesn't appear every single time I click on settings/icloud, but appears about 50% of the time

many thanks in advance

Ipad mini with retina display. IOS 8.2