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Sorry it's taken me so long to get back to you;
My suggestion would be to clone your templates. Delete all newbb templates, then regenerate them. Use the cloned templates as your default (you can set that in Forum Preferences).
Also, make sure you've placed the Koivi class in the Class folder.
One other thought occurs: if you change themes (which you can do for yourself only), does it fix the problem?
-Richard