For anyone who may have stumbled upon this forum and didn't find the calibre update solved their problem, like me. I've found a fix I think.....in Calibre change MOBI output defaults (personal doc tag) to [EBOK], and also make sure MOBI options are changed from (new) to (both) - having done that I managed to wireless transfer 3 books with no problems straight away and am happy to report all is working well
