Not certain why FritzBot ET does seem to replace the default north african campaign (the central european campaign was replaced because the railgun train was not supportable).
Campaign files have problems in ET in general. ET may reject a campaign if a map file is missing or if the first map in the campaign is not accepted (why no one knows). And if a problem occurs in a campaign file ET may even crash because the campaign error checking coded in ET is imperfect.
My suggestion is to make your own campaign files and see how that goes. A
recent topic on the Splash Damage forums covers campaign files nicely (or search these forums for previous posts).