So they can't see the portal in Cape of Distant Worlds? The update made the portal textures quite difficult to see, have they made sure they've checked every single one?
Also, make sure in your download, you included the .fhm file and they put it in exports, otherwise there will be no portal for them.
That's weird that it's not working for any maps for any of your friends.
First of all, make sure they're opening the zip folder and placing the contents in exports, not just putting the whole folder in there.
Secondly, make sure you're placing them in your LocalDisk>FeralHeart>Exports folder. Sometimes people make copies of the FH files or have copies of the game itself and misplace the files into the wrong version.
Also, an old issue that seemed to happen sometimes, is if you made a copy of your FH.exe file and pasted it onto your desktop to use as a shortcut, the portals won't show up. I didn't see this happen often, but if that's the case, try opening the FH game from within it's directory (AKA double click the .exe in your FH folder).
Have you tried changing your rendering subsystem? It's not usually the culprit of missing map portals, but it's worth a try.
Keep Warriorstrike's post in mind, the portals are veeery hard to see and can easily be passed entirely. Try downloading this texture mod that turns them more visible to the eye: http://www.feral-heart.com/smf/index.php?topic=55326.10