PDFCreator and VPN

I developed a program many years ago that creates PDF files, both with passwords and without passwords.
The language with which this program has been developed is the always valid VB6.
Now I have tried to access this program remotely (with a VPN) but the creation of PDF files no longer works.
If, on the other hand, I connect to this same program with Iperius or Supremo or Team Viewer everything is OK.
How to fix it?