Calibre frozen in middle of job

I made the mistake of trying to do a bulk transfer of 6 books from Calibre to my Sony reader. When I click on the whirling icon in the corner, the box comes up and reads 100% Progress but it's still whirling away. I try to stop the job but it comes up that you can't. I let it go for an hour or so but it still just kept going.
So I forced the disconnection.
Left it a few days. Tried again tonight and as soon as I went to the device library, it started again. It's been going for 1.5 hrs.
Obviously, it's frozen.
What do I do now?
thanks