this worked for me:
McAfee was blocking it for me. I had to allow the program in the access protection rules
Open VirusScan
Right click on Access Protection and choose Properties
Click on "Anti-virus Standard Protection"
Select rule "Prevent mass mailing worms from sending mail" and click edit
Add the program (calibre.exe) to the Processes to exclude list and click OK
See
http://www.symantec.com/connect/arti...-caused-mcafee