First of all, Thank You everyone for the posts in this thread. Thanks to reading through this thread, I was able to solve X10Net Interface Error without uninstalling AHP and losing the AHP registration, Modules, Timers, etc. I am using Windows XP Media Center Edition (SP3). Here are the steps:
1. Checked the Device Manager to make sure that the X10 USB Activehome device was present. (It was)
2. Checked Task Manager for the X10Nets.exe processs was running. I had to start it manually.
3. Renamed C:\Documents and Settings\All Users\X10 Settings\X10Active.xml
4. Downloaded and ran the install for the AHP Software.
5. When the question of "C:\Program Files\ActiveHome Pro folder already exists install anyway?" (or something like that), answer YES.
6. Completed the AHP Setup.
After completing these steps, AHP opened normally. I did not have to re-register AHP and all of my modules with timers and Macros were still present. One thing that I noticed strange with the dimmable modules though was that when I turned some of them on with the switch for the first time, the Dimming Slider was at 100% but the lamp was actually at around 10% brightness. I moved the Dimming Slider to 0% then back to 100%. After this procedure, the Module switch seems to be working normally again. I checked each one of my dimming modules and about half of them had this problem but all worked normally after moving the Slider on each module.
I hope that this simple procedure works for anyone that has this problem. And thank you once again to everyone who posted here.