ok, btw, try this instead of that script:
function bannCheck (nick, ip, username, serial)
local bt = tonumber(MySQL_GetString("Bann", "user_data", "Name LIKE '"..nick.."'"))
if bt then
if bt > 0 then
kickPlayer(source,root,"Du bist gebannt!")
end
end
end
addEventHandler("onPlayerConnect", getRootElement(), bannCheck)