I have a BaseForm which a bunch of other forms inherit from.  On the base form, I am referencing a Help dll which in turn references a HelpDB BO that uses a HelpDB DataSourceKey.  I can build and view the Base form just fine, but when I go to open and view the inherited forms I get DataSourceKey [HelpDB] not defined. I've commented out all code that uses the Help reference, but still get the error.  When I remove the Help reference completely it goes away.  How am I still getting this error even when I don't have code that uses the reference?

Even if you do not have any code that references a data source key, it might be that a shared property or shared method references the key.  Since the DataSources collection is stored in a shared variable, it exists in memory from the time that the application starts to the time that the application ends.  So, just by referencing the DLL, it could be trying to reference that key.