Plot hole: In Ben's nightmare, Gwen says, "We will come and get you!" and then she nags at Ben for being the one with the alien powers, and she does not join him in climbing the tree. My guess is that this was due to a script error; it was likely supposed to be "he" (i.e. Ben) instead of "we".
Factual error: It would be highly improbable for Kevin to find Vilgax frozen deep in space. As we see in first season's episode 'Secrets', Vilgax's ship was blasted apart in the upper atmosphere - after all, Ben escaped as Heatblast, and he wouldn't have been able to once beyond the stratosphere. Earth's gravitational pull would have kept Vilgax on Earth, not released him into deep space.
Continuity mistake: When Ben, Gwen and Max try to track down Ghostfreak, Max's scanner picks up "trace spectral activity from around that corner", which happens to be right ahead, but then Ghostfreak and cohorts appear from behind. In a deleted scene featured on the series' DVD, the source of the reading is revealed to be the tuba player Ghostfreak had possessed, who instantly runs off at the sight of Fourarms.
Other mistake: Generally, voice actors are listed only by the roles which they actually perform in the respective episodes. Even though Ripjaw's voice, Fred Tatasciore, voices Cannonbolt and others throughout the series, the character of Ripjaws does not appear in "Galactic Enforcers" and thus should not be listed in the credits.