When I select the 'create-link' button in FCKEditor, and you select the button search on server, a new browser window pops-up.

You cannot use this pop-up window, until you close the FCK link selection window first.

However, when you select an internal link and select ok, you get an authorization error.

I guess it has too do with the fact that the one window has to be closed.

My mistake, I was using Maxthon under XP and didn't notice that the popup blocker was active. When I switched to the standard IE, without any popup blocker it worked fine. Again tested it in Vista/IE7 and allowed popups for my site and again it works correctly.