This seems to happen after a failed install - some tables are created and then when you try to reinstall, it has a fit because the tables are already there.
Once on the failed install page, click on Continue to Load the Plugins page. Don't do anything yet...
Go into the database, rename all of the qtype table to their name with .old on the end. DO NOT just delete them as they do not always get recreated as they should.
Back to your Plugins page and click Continue. This should now go through without a hitch.
Return to the database and make sure that all the tables were recreated. I found that two were not - the qtype_match_options and the qtype_essay_options. So I renamed those two tables that I had renamed previously back to their original names. And this seems to be working.
(Before renaming these tables back to their original names, I had discovered that I couldn't open match questions.) After the rename, these work again.