Problem with SOAP receiver adapter? Please help!

Hi experts

I have the following scenario:

SAP R/3 -ABAP Proxy >XI--->SOAP --webservice

As you can see, I am sending data from R/3 system to XI via ABAP proxy. XI then sends data or calls a webservice via SOAP adapter.

When I test this scenario I am getting a error in the sxmb_moni that is,

"com.sap.aii.af.ra.ms.api.DeliveryException: TEXT/HTML; HTTP 504 Gateway Time-out"

I have checked the webservice url and it is working fine.

Can somebody tell me why am I getting this error message? How do I resolve this?

Thanks

Gopal