Hey there, I've been a map maker for years, so I'll try and help you.
You could try running the map and trying again on a different rendering system. Hit esc, go to options, and then hit video, rendering system, and select a different system. Restart the game and see if your map works then.
What kind of objects are nearby the portal? It could be that the portal isn't placed in a good area or the map itself may have a lot of objects.
If that isn't the case, try and place the portal in a different area. Make sure you get the coordinates of the portal as close as you can.
If that doesn't work, you could try renaming the map or seeing if any of the objects in your map may be causing problems.
