Thanks for the suggestions, Wisteso. Unfortunately, none of them are working. At this time, I'm going to chalk it up to either 1) Ubuntu 15.04 making some changes under the hood that were unfriendly (unless someone gets it up and running on that version), 2) running on an Intel 4400 HD chipset is a problem, or 3) some combination of the two.
Will keep tweaking on it and let you know if I find something that works.
Edit: BTW, this is a screenshot of how far I get into loading, and the error. Music running happily in the background:
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