When you install PC Access for Windows, the SETUP.EXE program asks you to insert each of your distribution diskettes into your diskette drive in sequence. Then it asks you to insert the first distribution diskette a second time (this diskette has a label that displays: "PC Access for Windows Disk 1"). The diskette you inserted does not appear to be this diskette.
If you inserted an incorrect diskette by mistake, remove it from your diskette drive and insert your "PC Access for Windows Disk 1".
If you have inserted your "PC Access for Windows Disk 1" and you continue to get this error message, follow the instructions for an Internal Error.