FWIW, I have a user here at work who is experiencing the exact same problem. It's like Parallels does not see her VM at all. The weird thing is that sometimes Parallels recognizes it - i think maybe the first time she logs in.
In I find out anything I'll let you know. But I plan to wipe and reinstall everything (Parallels and Windows XP).
1. Open Users/MACOS/Documents/Parallels/ folder.
2. Select Microsoft Windows XP folder and right-click (control-click) on it to open the contextual menu.
3. Select Get Info menu item.
4. Open Pwnership & Permissions option
5. Select Read&Write for access permissions.
6. Click Apply to enclosed items.. button.
7. Close Info window.
What I did was uninstall Parallels and reinstall it. It seems to work fine now. However, I would had liked not to do it all over again. It was a beta, so I am using on a stable version.