Not sure under what circumstances this will occur but I just ran into this on a Windows 7 64bit computer and thought I would post. After upgrading the computer from a 7.5.1 installation to 7.5.2 I was unable to open the Application architect. An error was displayed:
A module declared a dependency on another module which is not declared to be loaded; Missing module(s):
Sage.Platform.Extensibility.PlatformModule,
Sage.Platform.Orm.CodeGen.CodeGenerationModule (Sage.Platform.Application)
The solution to this problem was to uninstall the SalesLogix Admin tools and then reinstall them again (7.5.0) and then re-apply the service pack 7.5.2. After doing this everything seemed to work fine.
Update available that no longer requires editing the SalesLogix.xml file is now available. Details here: http://customerfx.com/pages/crmdeveloper/2009/10/14/announcing-git-extensions-for-saleslogix-and-the-customer-fx-open-source-initiative.aspx