O.k., I have just tried the following at my test-board:
I have installed the hack a second time, and I got exactly the same error as you wrote.
So you definetely installed the hack twice !!
How to get rid of this:
Deactivate both plugin-installations as I wrote in my posting before.
Moreover you must go to the table "datastore" and look there for the record named "pluginlist". Delete this record.
Then you can login to your board again.
Login into admin-cp, go to the plugin-manager, and click on "Save Active Status", to rebuild the entry in the datastore.
That's it.
And next time don't do any changes, when you already fell to sleep
BR
J?rg