In case anyone else has the issue with GeoDatabase Diagrammer running with errors:
I have ArcCatalog 10.0 and Visio 2013
I changed the Trust Center Macro settings to "Enable all macros" and Trust access to the VBA project object model checked.
This did not stop the errors.
I then went to the File Block settings and uncheked all the boxes.
Then the GeoDatabase Diagrammer started working.
I left Macro settings as I had changed them.
Hope this is helpful to someone,
Amy