HELP! I just connected my Passport for Mac and it thinks it's a MyBook and I can't see any archived data

I connected the Passport for Mac that I have been using as an archive disk for several months, an extra folder popped up on the Desktop called ‘EFI’ along with a folder called ‘MyBook’. Then up popped up a message box telling me the disk now has 2 partitions, did I want to eject both partitions or just the MyBook. I ejected both and tried opening the MyPassport on my other Mac and now I can’t see any data archived on it, just these two partitions. I have not ever partitioned the disk (I wouldn’t know where to even start) and I badly need to access the backed up data today so am in a panic!!! Any help appreciated.

Well that seems to have stumped people! I am still trying to work out what has happened. Disk Utility doesn’t seem to see anything wrong with the hardware, and there appears to be 66o+ MB of data that are on the disk but so far inaccessible.

Any help appreciated. Is this something a data recovery program might solve? Any suggestions?