'The registering device does not have appropriate credentials.' Facetime login issue.

'The registering device does not have appropriate credentials.' Facetime login issue.

The error message upon signing in is in the title ('The registering device does not have appropriate credentials.') in case you missed it. I'm absolutely sick of this- I've tried every solution I could possibly find:

-fiddling around with Flash Player- from deleting all site data and settings all the way to blocking all sites from storing information on this computer.)

-rebooting in safe mode

-rebooting normally (many times)

-checking internet settings (everything works fine)

-AppleID works fine when I log in to appleid.apple.com

-System Specs:

Model Name: MacBook Pro

Model Identifier: MacBookPro8,3

Processor Name: Intel Core i7

Processor Speed: 2.2 GHz

Number of Processors: 1

Total Number of Cores: 4

L2 Cache (per Core): 256 KB

L3 Cache: 6 MB

Memory: 8 GB

Boot ROM Version: MBP81.0047.B27

SMC Version (system): 1.70f6

-All software is up-to-date and all else works perfectly fine

It seems as though many people have been getting this recently- maybe something to do with an update?

I'm no where near an Apple Shop which makes everything all the more frustrating in terms of not being able to vent my anger towards the failure that I have to deal with.

Can anybody think of any other potential, recent fixes?

Many thanks,

K