I am running ArcGIS 10.2 and have Diagrammer 10.2. I have created a simple geodatabase and published the XML. When I try to import it into an empty personal or file geodatabase I get an error that says "Import xml data failed." I am just importing the schema, no data. This is a very simple database structure and I have not had this problem with past versions, only 10.2.
Also, when I run the Validate tool in Diagrammer there are no errors or warnings. But the Schema Report tool shows 3 errors that say "The element 'Extent' has invalid child element 'SpatialReference'. List of possible elements expected: 'XMin'." This is one error for each feature class.
I found a work around to this. I created a couple feature classes in a blank geodatabase, exported the XML in ArcCatalog, then opened the XML in Diagrammer. I could then manipulate it and publish it. Then use the published XML to import and build the schema is a geodatabase. Not sure why that works or what the original problem was but at least I can move forward for now.
I've exactly the same problem. The import fails and my schema is validated (no errors and no warnings).
As my schema has a lot of relationships already attributed it will be very long to redo everything. Did you find any solution other than publishing a simple gdb and build the new schema in this exported schema?