If you have tried fixes 1-6 and Error Code 1 persists, do not reinstall Windows. Do not pay for "VPN repair tools." Instead:

Sometimes, the root cause is not SoftEther itself, but the Windows network stack. Previous VPNs or power outages can leave Winsock or TCP/IP in a broken state, triggering generic errors like Code 1.

If you're looking for free solutions, consider the following: