Did you know that if you upgrade your OS from say Win95 to Win98 or from Win98 (1st Edition) to Win98 (2nd Edition), the SilkTest you enabled in your old OS are getting lost?
When the OS upgrade is completed most of your apps are still working including SilkTest. Even the Extension Enablers show that the extensions are still defined. But, when your ready to do additional windows declarations, for example, you'll notice that many of the CustomWin objects are back.

Solution:
Uninstall SilkTest, reinstall SilkTest, then reenable extensions.