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Iskariot - you can give calibre a 'dedicated' temporary location instead of having it share the common temporary location, see ==>>
http://manual.calibre-ebook.com/cust...ment-variables
This would enable you to easily exclude calibres temporary location from your AV, whilst letting it continue to monitor the common temporary location used by everything else.
Also if your using 64bit calibre then try installing the 32bit version (they can be installed alongside one another). Its overcome some other Permissions problems, I've no idea why.
BR