Unity Editor 'actively refused' attaching debugger

(Unity 3.2 / Monodevelop 2.4)

If I have the editor running, and try to 'attach' the debugger using the button in Monodevelop, I get the expected screen to select the process and debugger, but when it tries to attach, I get this error message:

No connection could be made because the target machine actively refused it

Any ideas what might be causing this and how to fix it?

This should be fixed in Unity 3.3

I am in the same trouble. Could please tell me how to solve it?

A possible solution to this is to ensure you are allowing the debugger to attach to the unity editor.

The check box to allow the debugger to attach is in:

Edit->Preferences->General->Allow Attaching Debugger to Editor

how to fix it. I am in same trouble