Print jobs sent from DOS to the LPT1: port are captured only when my Windows PC is connected to the internet
In order to capture the DOS LPT port in Mode 1, 2 or 3 (not in Mode 0), Printfil makes use of the Windows Networking Services.
Your machine does NOT need to be internet connected for this purpose, but if you'll find out that the capturing option works only when you're connected, then you're experiencing the "Media Sensing" problem.
Basically, this relatively new Windows feature continuously look for the presence of a psysical network connection. If it's not found, then the Networking Services are automatically stopped by Windows, so the DOS parallel port is not captured anymore.
This may happen if in the Windows machine there are no active network connections other than the "Internet" one, so Windows starts the Networking Services only when the machine is connected to the internet.
To solve this problem you can: