On Windows, run the installer with administrative privileges to ensure WinPcap/Npcap installs correctly. If you'd like to narrow this down, let me know: What operating system are you using?
The current standard, requiring a robust GNS3 VM. download old gns3 version
Old GNS3 versions may require specific, outdated versions of WinPcap, Wireshark, or Python that are hard to find. On Windows, run the installer with administrative privileges
Copy your /GNS3/Projects folder to a safe location. outdated versions of WinPcap
Ensure your GNS3 VM version matches your GUI version exactly; they cannot be mismatched.
Cleanly remove the existing GNS3 and its associated tools.