La opción es esta:
*NIX Server Load Limit
vBulletin can read the overall load of the server on certain *NIX setups (including Linux).
This allows vBulletin to determine the load on the server and processor, and to turn away further users if the load becomes too high.
If you do not want to use this option, set it to 0.
A typical level would be 5.00 for a reasonable warning level.
Y está con un 0... Voy a preguntar que pasa con la gente de vBulletin.