RFC_ERROR_COMMUNICATION: Connect to SAP gateway failed

HI All,

Im getting the following error while trying to call a RFC through JCO.

{0}#1#com.sap.mw.jco.JCO$Exception: (102) RFC_ERROR_COMMUNICATION: Connect to SAP gateway failed
Connect_PM  TYPE=A ASHOST=R3ip SYSNR=00 GWHOST=R3ip GWSERV=sapgw00 PCS=1

LOCATION    CPIC (TCP/IP) on local host with Unicode
ERROR       hostname 'R3ip' unknown

TIME        Thu May 15 12:13:36 2008
RELEASE     700
COMPONENT   NI (network interface)
VERSION     38
RC          -2
MODULE      niuxi.c
LINE        1529
DETAIL      NiPGetHostByName2: hostname 'R3ip' not found
SYSTEM CALL gethostbyname_r
COUNTER     1

I know it has something to do with the entries in the services and hosts files of the portal server. Please guide me on links from help.sap.com on this.