Parallels Desktop allows you to run Windows on Mac by opening the OS inside Mac. It is definitely convenient but that don’t make it error free. Here’s an error I encounter days ago, Parallels Desktop won’t start my Windows XP and prompts me this error message:

Virtual machine Microsoft Windows XP cannot be opened since it is already used in another Parallels Desktop windows.

Solution

For those of you who encounter the same message, here’s how I manage to re-open my windows in Parallel: Look for the .pvs file (which is most likely under Documents -> Parallels -> Microsoft Windows XP) and remove that file. Restart your Parallels Desktop and your windows should be working fine.