Failed to activate feature {GUID} at scope {sitename}

When I created a new web application at a custom port in WSS 3.0, the features on my old web site are NOT activated automatically.
But the features are listed anyway. When you try to activate them from site actions -> site collection features you got this error message:
Failed to activate feature {GUID} at scope {sitename}.
What you should do is to add the dll's of your features to your safecontrols list in your web.config file located in your site root. (namely c:inetpubwwwrootwss{portnumber})
You can copy them from your current site.