Looks like the issue only exist if you install MxModel Reflection and Excel Importer and/or Exporter in Mendix Studio Pro 10.1.1. I tested and there are no errors in earlier versions.
I found a solution:
Make sure that you are passing the correct parameter type ('MxModelReflection.MxObjectType') to the 'MxObject_Details' page. Verify that the data you are trying to pass as a parameter matches the expected type.
Double-check the setup of the 'MxObject_Details' page. Ensure that the parameter is correctly defined in the page properties and that the data source or microflow associated with the page is also properly configured to receive the correct parameter type.
Try running Mx Reflection again to ensure all your modules, entities, and attributes are synchronized and all up to date. This should hopefully ensure the MxObjectType is what Excel Importer expects.
I hope this helps.
I am facing the same issue, were you able to figure it out?
Hope it helps!