I have found it could be reproduced with a new Project:-
1. Add Data View
2. Add Data View Item
3. Set Data View Item's userAlias as "mydataitem"
4. In Data View, check useComponent
5. In Data View, enter "mydataitem" for defaultType
Error message then generated!
I did it with Architect 2.1 build 676 Windows version.
Really need help for this. It blocks my development progress. Thank!