WiX - CNDL0107 "invalid child element" in Product

When building a WiX file (tested with v3.8), you might see an error message similar to this one:


error CNDL0107: Schema validation failed with the following error at line 1, column 396: The element
'Product' in namespace 'http://schemas.microsoft.com/wix/2006/wi' has invalid child element 'UIRef' in namespace 'http://schemas.microsoft.com/wix/2006/wi'. List of possible elements expected: 'Package'. [C:\Dir\Test.wixproj]


This error might seem cryptic, but indicates that the schema expects Package to appear as the first element of the Product element.

Thankfully, there is a very easy fix for this error. The UIRef element (or whatever child element comes first in the WiX file) needs to be moved below the Package element.