Exchange 2003 and Global Catalogs

I am trying to decommission and old Windows 2003 box that is a DC and a GC. I know how to do this. I have already reassigned roles and I know the steps to disable the GC function and enable it on its replacement. However, when I disable the GC function on this old box, Exchange will not startup properly. It seems that Exchange 2003 has a bond with this DC/GC. I hope someone can tell me what I am missing. I did not find anything on Technet that was useful to me.