Yup, CTRL right click regenerates thumbnails, but only in CAS, more's the pity. If there are lots of thumbnails to be regenerated it is often quicker to delete the file, but if it's only a few, going through and regenerating them all one by one isn't too bad.
Thx for the solution... But I have already spent two hours locating and deleting those thumbnails I wanna regenerate in CASThumbnail.package