iPad Screen frozen with Not Enough Storage???

Help please...

My screen is frozen with the above message which underneath says This iPad cannot be backed up because there is not enough iCloud storage available (??)

You can manage your storage in Settings

Close Settings

I've had the below message quite a few times especially when I'm docked on my Sony RDP-XA900iP but normally tap on Close and that's it. I sync my iPad regularly to iTunes and backup to iCloud on that it seems with no problem.

Once it froze I tried turning off but will not let me swipe the 'slide to power off'. Connect to iTunes and it let me sync fine and download upgrades for my apps but no change to my iPad screen. Even changes the option from backup to iCloud to backup to computer and applied changes but still nothing.,,😠

Any ideas please.🙂