I found the solution in a pdf called "Parallels_Desktop_Advanced_VM_Configuration.pdf" (googled).
Basically it seems that Parallels needs all paths in its config.pvs file to be valid before it'll let you save configuration options. To access config.pvs, right click on the VM file and select "show package" which will reveal it. You can then edit the file to correct the paths using TextEdit.
Since my name had changed, I had three instances that needed correcting, a simple edit and save. One of the paths referenced a folder that no longer existed on my system, so I launched VM and got rid of it through the VM configuration panel. After these steps all is well again. It's possible that I could have manually deleted the path in config.sys but I decided to play it safe and do it through the Parallels Configuration panel.
I did open a support ticket, but I can't for the life of me figure out how to let Parallels know about it! I can't seem to login into the Request Tracker... Anyone?
Last edited: Jan 28, 2011