All Add-Ins "Missing"

Hi,

All of my Add-Ins in ArcGIS Desktop (10.2.2) have changed to [Missing] and none of them work. These are 6 different Add-Ins from different sources (including Esri). Most of these are Add-Ins I've been using for a couple of years, nothing has changed on my system. In fact I've been using these tools today, closed ArcMap and re-opened and they were gone. Another ArcMap session that was still open with those add-ins working, but no more as I just restarted my PC to see if that would fix it...

Any ideas what would make all my Add-Ins suddenly change from working and with correct icons to be not working and all with red [Missing] icons? How do I fix it? I have tried renaming my Add-Ins folder and my AppData Esri folder, however this hasn't made any difference.

I'm stumped. A couple of these add-ins are required for me to do my everyday work :(

Thanks,
Mike.