[The Goomba Mattress]

There's one problem: the StatsX plugin is being loaded twice. Remove the line:

statsx.amx ; stats

from the "Add custom plugins below" part in your plugins.ini file. It's already being loaded in the part with the default AMX plugins. Try amx_statscfgmenu again after removing the line from plugins.ini and see if that was the problem.

EDIT: Come to think of it, you shouldn't need any of the following plugins listed in your plugins.ini either:

ut_killing_spree.amx ; allows sounds
kill_announce.amx ; kill
humiliation.amx ; die
last_man.amx ; last man
ultimate_sound.amx ; sound
firstblood.amx ; firstblood

All of these are included in the StatsX plugin. Go ahead and remove them (or simply comment them out by placing a ';' in from the of the line) from your plugins.ini file.