Spark View Engine - Master pages are not found/loaded from Views->Shared folder

Question

I am adding spark to an existing ASP.Net application. Everything works expect for the following:

 I am unable to load/access ANY master pages from the Views->Shared folder.

Normal "shared" content in the Views->Shared folder is accessible and loads/works correctly. But ANY page that needs ANY master page (Application.spark or {some_master_page_name}.spark, fails with the following error.

 "Special node use had no understandable attributes"

This error is because the "page" is not properly formatted (because it does not have the master page content).

IF I MOVE the master page content to the spark content page - all works. I just can't get the spark view engine to find/load it as a master page/layout.

I have tired explicitly naming the master page to use, and that fails as well.

Hours of research and testing - no success. Hoping someone here will have run into this and found the solution.

Thanks!