Double Click - causes New Lister

I am new to this, and I am sure that the answer is quite simple but I can't seem to find it.

Everytime I double-click on a Folder, a New-Lister opens up, if my file is 8 deep in my filing system, in order to get to that file I have 8 new listers open on my desktop, and have to close the 7 other Listers.
(I would like to reach that file within the one same default Lister)

There must be something wrong in the Preferences but I can't seem to find it ... any help?

Are you by chance running Windows Vista?

If you are on Vista then Opus 9 (released on Friday) should fix the problem.

If you're not on Vista, try going to Preferences - Miscellaneous - Explorer Replacement and disabling Explorer replacement. OK the Preferences dialog, then go back into Preferences and turn Explorer replacement on again, and OK the dialog a second time.

If that still hasn't fixed it, go to Settings -> File Types and open the All Folders file type. Check the Open action (should be empty) and the Double-Click event (should be 'go').