DNN 5 - DotNetNuke.UI.Modules.ModuleHost.LoadModuleControl() throws NullReferenceException

Posting as a reference

when redirecting to custom controls in custom DNN 5 module, I get

InnerException: Object reference not set to an instance of an object.
Method: DotNetNuke.UI.Modules.ModuleHost.LoadModuleControl
StackTrace:
Message: DotNetNuke.Services.Exceptions.ModuleLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.UI.Modules.ModuleHost.LoadModuleControl()

From stackoverflow

• The problem was resolved by making sure that ALL custom controls inherit from PortalModuleBase