Uninstalling and re-installing seems a bit extreme if it is a setup that has been working for years. If the x10nets.exe file is missing, you have to ask yourself, WHY is it missing. Or did the file get corrupted and if so why? If it is missing, you could just request one of the forum users to e-mail you a copy of that file and try placing it in C:/Program Files/Common Files/X10 Common. Then run the file and see if AHP works.
There is the chance though that for one reason or another the service did not start. You can check this by clicking start>run and typing "services.msc" (no quotes). Once in services, scroll down to the bottom and find "X10 Device Network Service" and look in the status column. If it does not say "started", double click on that and in the properties box look at "Startup Type". If that is not set to Automatic, set it to that and click Apply. Then click the start button under "Service status" and click OK. Try running AHP again after that and see if it works, which it should.
Though uninstalling and re-installing would probably do the trick, I like to look for reasons why things happen. Missing and/or corrupted files can be a sign that possibly the hard drive is going bad. I work as a computer hardware tech and I see bad hard drives all the time. Not saying that your drive is actually failing, I would try the steps above first and if that does not work, do as Dan says and uninstall/re-install after backing up your .ahx files. If you continue to have problems though I would look into scanning your hard drive for errors.
