As of the end of July 2013, X10.com (X10 WTI) is no longer in business. A company called Authinx Inc appears to have taken over the business under the name x10pro-usa.com. It provides some information about the demise of X10.com.
Partial Solution to Keeping ActiveHome Pro Alive?
Tuicemen.com's forums provide partial solutions to install or reinstall the North American versions of ActiveHome Pro while the software servers are down. A copy of the ActiveHome SDK is available from that site. If you own a CM15A or CM19A and want to use them in Windows, download that kit if you haven't done it before. Other Windows software seem to be able to work with those transceivers through the device drivers and activeX components in the kit.
The ActiveHome software (which worked in Windows 3.1 and Windows 95, 98) is offered alongside the CM19A. It is not clear how this is supposed to workd, ActiveHome is for the CM11A a serial RS232 device and the CM19A connects through USB.