PRS-300

I just received a second-hand PRS-300 from a friend. I have a Mac Book Pro, had not trouble installing the software and using it, however the e reader itself will not communicate with the soft ware. It's not locked and the Sony instructions have not been helpful! It appears on the list within the soft ware but is named 'error'. I can successfully open and install ebooks on the same device using calibre. I would really like to buy some books from the sony store before I go away though!

Thanks!