HTTP response contains status code 503 with the description

<SAP:ApplicationFaultMessage namespace="" />

<SAP:Stack>HTTP response contains status code 503 with the description

Service Unavailable Error when sending by HTTP (error code: 503, error

text: Service Unavailable)</SAP:Stack>

<SAP:Retry>N</SAP:Retry>

</SAP:Error>

Please advice. Initially we thought the J2EE services were unavailable . But now even when the services are running we still have the same issue when there is a http call from an external application to XI . The message get posted but there is an error on the response back to the external application.

Even the contract which was supposed to be created in ERP from the external application did not get created.

Please advice.

Thanks,

Nivedita