I vaguely remembered having much the same problem at some point, and looking at my notes for OpenFTS installation I found this statement:
"Also may have to manually drop the txt table if it's been copied in from the template DB [template1], otherwise 'DML failed - relation txt already exists.'"
This is from about 6 months ago, so its not that fresh in my mind, but I think that if you follow the OpenFTS installation instructions and source openfts.sql into your database, it creates the txt table, and so you have to drop it before the driver can initialise properly. I can't offer any guarantee that this is the best possible action, but I seem to remember it working OK.
