The error has nothing to do with the application name issue you refer to - at least I can't imagine how it could. In order to have the membership records you said you have in those tables, you must have run the GSP install wizard where one of the applicationName attributes was set to Gallery Server Pro. Since you changed the name, those records are no longer necessary and you may delete them.
That is helpful to report the line of code where the error is occurring, but it is baffling why it should fail. Here it is, along with the preceding line:
Code:Type metadataExtractor = assembly.GetType("GalleryServerPro.Business.Wpf.WpfMetadataExtractor");
System.Reflection.MethodInfo addMetadataMethod = metadataExtractor.GetMethod("AddWpfBitmapMetadata", parmTypes);
We can conclude GSP is finding the GalleryServerPro.Business.Wpf.dll but, because metadataExtractor is null, cannot find the WpfMetadataExtractor class inside it. Did you happen to change the namespace and/or class name in the WPF project? That is the only explanation that makes sense.
If that's not it, I don't know what else to suggest except to go back to the drawing board and put your testing cap on. Start with a standard GSP release and get it working. Then slowly modify it by editing web.config, etc, until you arrive at your current app setup.
Roger Martin
Creator and Lead Developer of Gallery Server Pro