I shut my computer down without closing Angry Birds properly. I got a load error the next time that I opened it which said something along the following lines: “attempt to index global 'flurry" (a nil value) (call stack not available)” Here is how I fixed it. I am using Windows 7 64 bit Professional. It should be very similar for Vista.
1. Let's find the Appdata files for Angry Birds!
I went to my C: Drive and in the upper right hand “search” box, I typed Rovio. I have the program actually installed on a different drive, but your appdata is almost always stored on your C: drive. You’ll know you got the correct folder when you open it and it shows another folder labeled “Angry Birds”. When you click on this “Angry Birds” folder, it should have another folder named “updates”, and three files, bi_data.lua, highscores.lua, and settings.lua.
2. Once you locate this correct folder, rename this Rovio folder Rovio I.
3. Open Angry Birds again and it’ll ask you for your key.
4. Enter your key and activate your version of Angry Birds.
5. The program will have created a new Rovio folder. Return to your Rovio I folder and copy the highscores.lua file from it into your new Rovio folder, in the Angry Birds folder (same place it was located before). Voila!
6. Mine works perfectly now.
Update: I just noticed by retracing these steps that Rovio puts all of your versions of Angry Birds in this "Rovio" folder. I have since added Angry Birds Star Wars since I first wrote this. If you have more than one version of the game installed, might I suggest renaming the specific game folder and moving the files that way?