I have been using version CS6 since its launch. I had my operating system upgraded to Windows 8 in the New Year and loaded my programs afresh then.
I used Illustrator extensively in April and May and haven't used it much since then. Yesterday, when I came to do some work with it, I couldn't start a new document without this message appearing, after clicking OK the program became unresponsive (an operating system 'ding' sounded on each mouse click) and could only be closed using Task Manager.
I managed to open a new file from a template or open an existing PDF. However, when I tried to save it under a new name, the same issue happened.
I can only think that whatever is causing this happend after an update between now and last May/June as I was using the program freely before then.