Recently I accidentally logged off (rather than shut down) a Parallels VM for which I hand not written down the password, er, well, I wrote down the password but not what it was for.
So I figured I'd restore the Time Machine backup for the .pvm file (Parallels Virtual Machine) from the day before (I hadn't used it for several weeks) and I figured I'd be OK.
The first issue is that Time Machine takes about 30 to 40 minutes to restore a 25Gb virtual machine.
Unfortunately during that time the machine is basically running flat out in some kernel process so that you can do virtually nothing else. This can be further aggravated by having Carbonite (which I also use) and/or Time Machine running backups.
Its best to turn these two off before starting anything like this.
Once the file is fully restored to disk by Time Machine I figured I'd just double click it and have it work.
Boy, was I wrong...