SQL & PL/SQL

Hello !
I am trying to activate a web service located on a remote machine inside a database trigger . This WSDL has been generated by a XI (SAP) tool and located on the server on which the XI is installed.
XI is an EAI tool a product that is included in the SAP products - for integrating between SAP and other tools - including Oracle DB.
When I try to call the web service using UTL_HTTP package - a procedure i wrote correctly - I get the following error message :
"
ORA-29273: HTTP request failed
ORA-06512: at "SYS.UTL_HTTP", line 1029
ORA-12545: Connect failed because target host or object does not exist
"
I have GOOGLED the last message ( ORA-12545) , but the forums referred to a client for ORACLE, which is configured incorrectly; none of them referred to my case - calling a web service. BTW I tried using the web server's IP address instead of the DNS but got the same error.

Any suggestion would be very appreciated.

Best Regards,
Shimon B.