have a mac mini, just upgraded to os X6, had an wd passport and it stopped backing up/being recognizedby wd utilities and by mac disk utilities, bumming me out, can't backup.
As @i7Baby suggested, you should upgrade the drivers.
Also check if your firmware is up to date: http://www.wdc.com/wdproducts/wdsmartwareupdate/firmware.asp?id=wdfMyPassport&os=WIN
You can also try a different cable and another mac with the OS version you were using before you upgraded?
If it is recognized there, back everything up from the drive and reformat it:
http://wdc.custhelp.com/app/answers/detail/a_id/291/
Here's something from the WD knowledge base that might help you as well: http://wdc.custhelp.com/app/answers/detail/a_id/505
As @i7Baby suggested, you should upgrade the drivers.
Also check if your firmware is up to date: http://www.wdc.com/wdproducts/wdsmartwareupdate/firmware.asp?id=wdfMyPassport&os=WIN
You can also try a different cable and another mac with the OS version you were using before you upgraded?
If it is recognized there, back everything up from the drive and reformat it:
http://wdc.custhelp.com/app/answers/detail/a_id/291/
Here's something from the WD knowledge base that might help you as well: http://wdc.custhelp.com/app/answers/detail/a_id/505