Thread:Extension talk:Push/Fatal exception of type MWException

I just installed Push on an older v1.20 wiki, using git:

git clone https://gerrit.wikimedia.org/r/p/mediawiki/extensions/Push.git

I'm trying to use it to migrate only specific articles to a new v1.23.6 wiki running on the same server, but with a different domain name, in preparation of retiring the old one that has some "vandalism" on it.

As soon as I put the extension in place, and updated the LocalSettings.php the "Push" tab shows up with what appears to be the proper configuration for the new wiki to push to; however, if I try to push a page to the new one, it grays out the button, but never does anything else. The page never gets pushed. If I go to the Special:Push page I get this error message on the page:

[8562cc04] 2015-05-02 04:15:09: Fatal exception of type MWException

Any ideas on why I'm getting this?