Daniel,

Putting this answer here so I can include links.

In the Mendix Cloud, you can access your application logs.  Directions here:  https://docs.mendix.com/developerportal/operate/logs

You could also search for the text in the error message in your app in Studio Pro.  In the Edit Menu, select Find (or use Control + F if you’re a fan of keyboard shortcuts).  They type in some part of that message and see if you get any results.  This would give you a starting point for figuring out what is causing the problem.

Mike