The error mentions a problem in your installation. Try reinstalling Marmalade.
BTW you need .mkf (Subproject) file so that your extension can be linked as a subproject to the marmalade project. If you're having just a mkb that means you're doing something very wrong. The extension must have two mkbs one s4e and one mkf file. Take a look at one of the prebuilt marmalade's extensions and compare where's the problem.
One more thing, extension project doesn't work well with Marmalade Hub. You don't actually need Hub at all. You cannot open any extension in Visual Studio, so it's a waste if you want to import the extension to the hub. Although extension making in OSX can be easier if Hub is used, since XCode works well with extension projects and sometimes needed to make .a and .o files.
Anyways try double clicking extension.mkb then extension_andoid.mkb and see if it gives any error or not.