I know that Evan ran into a similar problem, to which I responded:
I'm not sure what's up with that. It might be a problem with not finding your Java virtual machine. You might mess around in Eclipse to see if anything jumps out.
Specifically, right click on the project and choose "properties", then choose "Java Build Path", and check the "Libraries" tab to see if "JRE System Library" is listed there.
Sometimes problems like these can also happen if you had the wrong folder for the project.
You might try:
a) Posting to the Q&A to see if anyone else has gotten this problem.
b) Restarting Part 3 of the lab, and trying the steps carefully again, to see if it happens again.
c) Sending me screenshots of your problem.
d) Googling for "Eclipse" + the error messages you're seeing.
Or, I can take a look in person on Monday morning.
However, I don't know whether any of this helped resolved that issue or not. I will email Evan to about this question on the Q&A.