This morning when I tried to open any of the three sites I had previously created using VSD, none of them would open! I got an error report window (which I selected "send error report"). A complete reboot did not resolve the problem.

I went to get coffee an contemplate "what am I going to do now?"

I decided to start VSD without calling up one of my projects. It came up fine. Then I created a new "dummy" project and then closed it without adding any content. Next I called up my most recent project and it came up without any errors too. Jubilation rang out in the office! That said, it was a little "tense" around here for a while!

One change I had made to the computer (XP Pro sp3) yesterday after finishing with VSD was to download and install Open Office 3. I'm not certain whether installing Open Office had any bearing on the ability to open my projects or not.

I didn't find any mention of the "won't open" dilemma when I searched. Are there any tips for me if this happens again and I'm not as "lucky" as this morning?

I had this happen some time ago on my laptop (Vista). Searching the forums I found the suggestion to right click and choose run as administrator. It opened right up. After a few times, it went back to opening normally. I also got it to open by going into my files and clicking on the .vnu in the actual website folder.
I would suspect something that came with Open Office is causing a glitch. In my case it turned out to be some left-over bit from Norton Anti-Virus. Norton did not play nice with a lot of the programs on my computer so I removed it - but didn't get rid of it completely. Now that it's all gone, everything opens and runs just fine. I use AVG now, but I make sure it's not running a scan when I want to open something.