Hi @Anonymous
The most common cause is a version mismatch between the Modelo Revit plug-in and the Revit version you are using.
As the first step, I would suggest checking the Desktop App to see if there are any Revit updates available. For information on using the Desktop App see the following article: About the Autodesk Desktop App
Note: If you are not able to download updates through the Desktop App, the following article has information on downloading updates through the Autodesk Accounts page:
Install Updates, Add-ons, and Enhancements
Secondly, if this occurs only on one machine, then I suggest that you find another machine that has this plugin that does not get the error message when opening Revit and copy the config.ini from the C:\Users\user name folder\AppData\Roaming\Autodesk\Modelo\RevitPlugin and copy it to your machine.
If you find posts have solved your problem, please click on 'Accept as solution' to help others with similar questions. Thank you.
Regards,