Login failure error when sending message from PI to webservice

Hi Experts,

We have a scenario where sending messages from PI to a web service. Getting the below error in sxmb_moni.

<?xml version="1.0" encoding="UTF-8"
standalone="yes" ?>
- <!--
Inbound Message
  -->
- <SAP:Error
SOAP:mustUnderstand="1" xmlns:SAP="http://sap.com/xi/XI/Message/30" xmlns:SOAP="http://schemas.xmlsoap.org/soap/envelope/">

  <SAP:Category>XIAdapterFramework</SAP:Category>

  <SAP:Code area="MESSAGE">GENERAL</SAP:Code>

  <SAP:P1 />

  <SAP:P2 />

  <SAP:P3 />

  <SAP:P4 />

  <SAP:AdditionalText>com.sap.engine.interfaces.messaging.api.exception.MessagingException:
SOAP: response message contains an error
XIAdapter/PARSING/ADAPTER.SOAP_EXCEPTION - soap fault: Logon failure: unknown
user name or bad password.</SAP:AdditionalText>

  <SAP:Stack />

  <SAP:Retry>M</SAP:Retry>

I have checked the communication channel. The url we are using it is opening fine with the user id and password maintained but still getting the error in communication channel as below.

Delivery of the message
to the application using connection SOAP_http://sap.com/xi/XI/System failed, due
to: com.sap.engine.interfaces.messaging.api.exception.MessagingException: SOAP:
response message contains an error XIAdapter/PARSING/ADAPTER.SOAP_EXCEPTION -
soap fault: Logon failure: unknown user name or bad password.

Can any one please suggest the possible reason and how to correct ?