Article needs to be relabeled as lost
From The Lost Media Wiki
I just found out why the YouTube links don't work anymore.
I clicked PopTeenToons' YouTube channel to open in another tab, and it seems the channel has been retooled for some time with new content and the episodes of Butt-Ugly Martians nowhere to be seen.
As I've said in my previous comment, I've found other sources where one can watch episodes of Butt-Ugly Martians, but not every episode is accounted for.