rdisp/wp_no_spo_Fro_min parameter

I have a problem with printing using access method F : Printing on fronted computer. Only one spool work process in each server can be used for this printing method.

I read the article about printing at http://help.sap.com/saphelp_nw04/helpdata/EN/91/0cfe3b9f0bd274e10000000a114084/content.htm. When I try to set the rdisp/wp_no_spo_Fro_min parameter, there is a message : The parameter name is not known.

How to solve this problem? Is there other solution rather than setting the rdisp/wp_no_spo_Fro_min parameter or there are the solution how to set rdisp/wp_no_spo_Fro_min parameter.

Thank you