I tried downloading different versions of the Excel Exporter and the Model Reflection, but was not able to reproduce your error. My advice is to upgrade Studio Pro to the latest MTS version (10.18.x at the moment), and download the latest versions of both Excel Exporter and Model Reflection from the Marketplace both v8+. This should resolve any issue you encounter.
Good luck!
Johan
Yes, I have already installed MxModelReflection while working on the Excel import.
It is an It is an MxObjectType_Select page, which is part of the Mx Model Reflection module