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					Originally Posted by  Erykz
					 
				 
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I've been using calibre for years without any problems. I don't see what could suddenly cause this problem. 
 
I don't understand what you mean. 
			
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 I suspect @theducks is referring to the calibre library - however, the editor operates on a copy of the EPUB that it creates in its cache folder, which is normally in C:\Users\****\AppData\Roaming.
Where is your library?
Try copying an EPUB to the desktop and editing it directly via Windows Open with ==>> C:\Program Files\Calibre2\ebook-edit.exe.  If that works it would suggest your problem is related to the library.
What version of calibre were you using before this problem appeared?
BR