Does it happens if you run spchapi.exe directly? You can use fre Regmon utility from http://www.sysinternals.com/ntw2k/source/regmon.shtml to monitor registry access. It could give you an idea what the problem is.

>I am using the spchapi.exe in my installshield setup to install the speech engine. The spchapi.exe is executed as a custom action after the 'Create Shortcuts' option.
>The problem is that on a Windows 98 machine, the xvoice.dll file does not get registered. The folder is existing and the file is also existing in the windows\speech folder. If i manually right click on the xvoice.dll and register, it registers successfully and there is no problem in my software. This problem only happens on Win 98and works well on an XP OS.