PC Access believes you have already registered your copy of PC Access. This should have created a license file, PCAWIN.LIC. This file should exist in the same directory where your PC Access executable file (PCAWIN.EXE) exists. However, PC Access cannot find your license file there.
Check your PC Access for Windows - Disk 1. When you installed PC Access and filled out the Register PC Access for Windows window, PC Access should have prompted you to insert your Disk 1. PC Access should have then created a backup copy of your license file there. You should be able to copy it from your Disk 1 to your PC Access executable directory.
If this message persists after you copy your backup PCAWIN.LIC file to your PC Access executable directory, or you cannot find your backup copy, follow the instructions for an Internal Error.