Terry, I'm assuming that Site Mate is installed on a CE device such as an iPAQ. Typically this error means that somehow Site Mate got installed in two different locations. If the iPAQ only has Site Mate on it, do a hard reset by sliding open the little door on the bottom with your stylus. Then flip the small switch to the side and flip it back. This will reset the iPAQ and completely erase everything on it. You should then be able to reinstall Site Mate and run with no errors.
If you have other programs and/or files you want to save, put the iPAQ in the docking cradle and run Windows Explorer on the Desktop computer. Scroll down and open up the folder for "Mobile Devices". This will show you all the files on the iPAQ. Find all installations of Site Mate and delete them then reinstall.