There is a bug in the Map Creator Part 1 v18.104.22.168 package that causes that error. Short of fixing the bug and recompiling the package, there is no way to fix it.
The bug does not exist in Map Creator Part 1 v22.214.171.124. If you run that, you will not have that error. For what it's worth, I don't believe there is any significant difference between v126.96.36.199 and v188.8.131.52 of Map Creator Part 1; the differences between the two versions all lie in Part 2.
So, simply install a copy of Map Creator v184.108.40.206, but do not uninstall v220.127.116.11. Then use Part 1 from v18.104.22.168 for the map files, and use Part 2 from v22.214.171.124 for the XML file.
However, the Map Creator within TripleA (accessed through the "Engine Preferences" button on the startup window) replaces all the functionality of Map Creator Part 1, so it is not really necessary to install v126.96.36.199. at all. And, of course, you can still use Part 2 of v188.8.131.52 after you have set up your map files to set up your XML file.
Just remember that a lot of features have been added to TripleA since v184.108.40.206 was released, so you're still probably going to end up extensively editing your XML file by hand, anyway, after initially creating it with Part 2, and any newer features you add manually to the XML file will cause Part 2 to crash if you try to load the modified XML file into it.
Why search for artificial intelligence when there's such a crying need for the natural kind? — Michael J. Flynn
In Triplea 1.9, the prerelease, on the main screen there is a 'settings / preferences' button. click that, you should see a button to launch the old map creator, and another to launch the new one (labelled as in beta).
The new one has some issues, and the old one does too. There is work to be done to fix them both, but right now efforts are more on the game engine proper side... Not enough people to work on everything that needs to be done.