In order for 3ds Max to use an action table, it need to be registered. For most plug-ins, this is done by returning it's action table in the following methods in the plug-ins class descriptor:

virtual int ClassDesc::NumActionTables();
virtual ActionTable* ClassDesc::GetActionTable(int i);

The system will call these methods on start-up, so if your plug-in exports action tables, it cannot be dynamically loaded. This is required because the action items need to be displayed in the customization dialogs even if your plug-in is not in use.