I can't for the life of me figure out where that local xampp path is coming from. That's clearly the problem, but it's not coming from the System Setting and the only other way it should appear at all is if the devMode system setting is on. And I'm not getting it at Bob's Guides where the current version of UGM is running. It's a puzzler.
One thing left to try.
In the core/components/upgrademodx/model/upgrademodx/upgrademodx.class.php file add these lines at the end of the init() function (just before the closing brace near line 157):
$cm = $modx->getCacheManager();
$this->versionListPath = $cm->getCachePath() . 'upgrademodx/;
You might want to re-install UGM first to get your other system settings back.