Can’t start Rhino: "Input is not a valid base 64 string" error

Hi, wondering if anyone could help me out with this error:


This occurs on start-up of Rhino - before hitting the “sign in” screen. “Retry” leads nowhere, “close” lets you obtain a license but the app itself wont load…

Troubleshooting attempted:

Reinstall Rhino
Force remove existing version (7.24) using geek uninstaller (removes leftover files/registry entries) and reinstall latest version (7.28, downloaded from webstite)
Run all pending updates and reboot windows
Run .NET repair tool suggested here
Verified graphics drivers are current

Any assistance or ideas would be appreciated.

I would try running a “repair” instead of a reinstall, so all of the required redistributable tools from Microsoft are installed.

Any luck?

Hi John,

Thanks for the quick response, no luck running “repair” I’m afraid.

That indicates your Windows setup is pretty messed up.

If it were me, I would do the following:

  1. Temporarily disable any local antimalware tools.

  2. Run the combined 2015, 2017, and 2019 installer using this link from Microsoft:
    Latest supported Visual C++ Redistributable downloads | Microsoft Learn
    Use the 64-bit tool since Rhino is a 64-bit application.

  3. Run the .NET repair tool from Microsoft:

  4. Repair Rhino 7:
    a. Windows Control Panel
    b. Add/Remove programs
    c. Select Rhino
    d. Click Change
    e. Click Repair

Don’t be surprised if you need to restart Windows.

Any luck?

That indicates your Windows setup is pretty messed up.

This seems to have been it. On closer inspection we found other windows bits not functioning properly (eg Sysinfo was giving WMI related errors), and other similarly ambiguous application errors started cropping up. Rhino worked with another user account on the same machine, so perhaps a corrupted user profile was the culprit.

In any case we’ve decided to wipe and reimage the problem machine rather than spend more time troubleshooting this.

Thanks for the help!