>Trying to install compiled application (VFP6 - SP3) using Intall Shield Express to NT 4.0 workstation. Getting an error message that file COMCAT.DLL will not self-register. Does anyone know what this DLL does and why it might not install properly? TIA.

COMCAT is the Component Category manager. The probability is that the self registration failed because (1) you're attempting to register it out of order (ie it installs along with some other .DLL that must be registered or copied in place before it can self-register) or (2) the logged-in user doesn't have the necessary access permissions to update the portion of the registry used for self-registration (most likely if you're logged in as a non-Admin user and any security has been imposed on the registry.)