JCO connection getting expired when system restart...

Hi experts,

I configured the JCO connection.It worked at first time..when i restart the system...It gives the following error

com.sap.mw.jco.JCO$Exception: (102) RFC_ERROR_COMMUNICATION: Connect to message serverhost failed Connect_PM TYPE=B MSHOST=Hostname GROUP=SPACE R3NAME=D MSSERV=sapmsDEV PCS=1 ERROR hostname '?' unknown TIME

Fri Dec 21 04:25:25 2007 RELEASE 640 COMPONENT NI (network interface) VERSION 37 RC -2 COUNTER 1

I have to configure the jco connection each and every time when restart the system..Please tel me what may be the reason..

Thanks & Regards

Mathi