I took a peek at the gg_knife_pro.py code and noticed what looks like a bug in the code but I'm not familiar with python sythax:
(Notice the "\" in the conditional statement line# 122 of gg_knife_pro.py)
# If the level difference is higher than the limit, stop here
if (attackerLevel - ggVictim.level) > int(gg_knife_pro_limit) and \
int(gg_knife_pro_limit) != 0:
msg(attacker, 'LevelDifferenceLimit',
{'limit': int(gg_knife_pro_limit)}, prefix=True)
return