I searched the forum and didn’t see this. This may be more of a Revit forum question, but thought I would ask here since it’s affecting Dynamo. Has anyone ever encountered this error message? It occurs in all versions of Revit when trying to run any script. Also, Dynamo will not open.
Disable all Revit add-ins until you find which add-in is triggering this.
You might also find something in the journal, I recommend triggering the popup and leaving it open.
Once you know that reach out to the developer of the add-in to find a resolution.
Thanks for the response @jacob.small . Yeah, I did check the users add-ins and there wasn’t anything additional installed that other users who are not getting the error, didn’t have installed. I will check the journal.
The order of loading and the combinations of add-ins matter.
I can build 300 add-ins that work perfectly until you install number 150 and 175, and suddenly crash/warning/error city.
These are the only add-ins the user had installed and if I’m not mistaken all of these are standard with the Revit install.
Bluebeam is not standard and can cause issues like this, though rarely. Also add-ins don’t need buttons. They can be silent and have no UX need and therefore no button, or tbh could be under the external tools dropdown.
To identify which add-ins are loading you can usually search the journal for the lines with ‘vendor id’. I recommend the journal from a clean first first time installation (before you put any customizations in there) and archiving it to compare API_ERROR lines and Vendor Id lines as that identifies the root cause of 75% of the issues I used to see in support.
Okay thanks for the input. I will investigate and provide a solution here…if I find it. 
If you post the journal here I can have a look for you. You can also rename your DynamoSettings file and packages folder to something else to quickly remove all Dynamo customizations which can help in these instances.
The issue is on another users computer and not mine, so getting the journal and/or renaming the settings file may be a slight challenge. I will keep you posted.
Hey @jacob.small, I had one last hunch about the issue and turns out that was it. I am using Dyno browser to incorporate the scripts into the Revit toolbar. I created batch files to use for updating scripts, definitions and packages. I also have a batch file that copies the Dyno config file to the user’s Appdata folder. I have customized the Dyno config file to look at specific folders, so it’s easier to run the batch file versus having the user install the Dyno browser and then have to overwrite the config file. Turns out, the user got a new computer and never ran that batch file. So technically Dyno wasn’t installed at that point. They ran the batch file and are now able to run Dynamo and the scripts.
Thanks again for taking time to help investigate the issue!! Will mark this post as resolved.