Well it could be many different reasons, but most likely it is a program starting when you start windows, and it causes an error in the registry

Here is something to try:

1. Boot into safe mode. To do that, hold the Ctrl button while your BIOS does its stuff when your computer is booting up, and hold it while Windows is starting up until you get to the boot menu (Basically turn your computer on and hold Ctrl until you see a menu). From the menu select "Safe mode" (option number three).

2. If you still see the message once you get into windows, there is probably something gone wrong in windows itself, and you may want to consider reinstalling windows. If not...

3. It is definitely caused by something normally starting up when windows boots. Click Start-->Run and type 'msconfig'. Go to the 'Startup' tab, and uncheck everything. Now reboot the computer normally. If it starts up without that message, then you know it was one of the things that you unchecked. You will have to use process of elimination to figure out what it is, and it could be a combination of some too. If you still get the message though...

4. It is caused by something normally starting up before the GUI is loaded. Put everything back in the msconfig startup tab (because it is unhealthy for computers to have nothing starting up, especially important things like virus scanners and the like) and reboot back into that menu I mentioned in #1. This time though, choose Step-By-Step confirmation. Go through and say 'no' to everything until you get to 'WIN,' where you should choose 'yes'. Then say 'no' to everything again. If the message doesn't appear, then it is time for process of elimination.

5. After you figure out what program is causing the problem, either get a patch, or uninstall it.

Remember that these are only guidelines. There may be other combinations (like it could be a combination of something starting up before and something starting up after). Or it could be something else. Use your logic and computer skills and only use my help as a starting point.