I have MW 1.22.6 and I have encountered this problem.
I do not understand how to solve it. I commented the line 7 in WikiFarm_body.php, but the problem persists. What is wrong?
Topic on Extension talk:WikiFarm
Appearance
These functions must be commented in the 6-7 classes, so probably the error message changed a bit and is something like /extensions/WikiFarm/WikiFarmStatistics/WikiFarmStatistics_body.php.