Resource (.resx) file Key naming conventions?

Just use Pascal naming convention. Dont attribute the key to a module or the class. Generalize it so that it can be reused.

Eg: ReadWriteWarningMessage

The dot separated convention works fine for menu items. But what about strings that are generated dynamically or user messages.

have you considered underscores like Menu_File_Open or something like Place_StringDescription? I currently employ a scheme where common stuff go to Common_ like Common_PressHereTo and view specific go to their respective place like MainMenu_FileOpen. In general, before the underscore i type where the Resource appears and after the underscore a descriptive text.