Can not increase the Max pool memory from tomcat5w.exe for a tomcat servic

I have a tomcat service on a windows 2003 server. I have a 4G RAM on this server machine. When I try to increase the Max pool memory from the tomcat5w.exe tool by inserting 2000 in the Max pool memory text field, and try to restart the service; it gives me an error and the service does not get restarted.

Does any one have any suggestion or has experienced similar problem?

Thank you in advance