Email templates not appearing in dropdown list

Email templates not appearing in dropdown list

I have a number of email templates which I use on an on-going basis. Since yesterday when I attempt to select an email template from the dropdown list I can only get 'None, - the system is not allowing me access to my templates as it had been doing. This has happened occasionally before but it would correct itself after a few attempts. I haven’t made any changes to my settings (as far as I know!). Can anyone advise?