I have the exact problem. Ever since updating to Yosemite I was unable to use Parallels Mounter on any of my images or hdds, including a Windows 7 and Debian machines.
Parallel Mounter says:
Parallels Mounter is unable to open the virtual hard disk.
Either the hard disk has no volumes or its file system is not supported or contains errors. Start your virtual machine and check the disk for file system errors.
No matter what combination of sharing settings I choose in the virtual machine configuration there is never a /Volumes/C mount so I can't access my Windows files from Mac.
Parallels has broken this in version 9 and there is no way to fix it. Some people byte the bullet and upgrade to parallels 10 for a fee but I think it is unfair to break a feature and require payable upgrade for the fix.