I am developing a NWC workflow with a Start Form.  The form contains some typical controls: several Labels and Spacers, one Data Lookup, several Choice - Single, a couple Yes/No, and three File Upload.

From the Designer workspace, I click on "Workflow Testing".  The form launches and I fill in the data, select choice fields, y/n, etc. and add several attachments.  Once done, I press the Submit button.

The workflow fails almost immediately after Submit is pressed with "Semantic error(s) found. uError Code: Semantic.Error]".

What are Semantic errors, and how do I troubleshoot the Workflow to determine the cause of the errors?