VMware 10 - can't map physical disk as writable

Using 10.0 on a Win 7x64 host, I created a Win 7 VM from a physical disk.  I edited the vmx and then took a snapshot of the VM.  I can map the physical drive, but I cannot map it as writable.  If I uncheck the read-only box and try to map the disk, I receive a message that "there was a problem trying to map the virtual disk volume."  See the screenshot.  In Version 9, I could take the same steps and map the physical drive as writable.  Is there an edit or tweak to get around this?  Thanks.