Hi,
We encouter this error recently (it was working 3 months ago) while trying to connect to salesforce SOAP service method; importProducts.

Do you have any idea why this happen?
Error:
System.ServiceModel.FaultException: INVALID_SESSION_ID: Invalid Session ID found in SessionHeader: Illegal Session. Session not found, missing session hash: cWDoKsK9fIn01hr05uV2ZaCI+c6Q1iuM4xAtxMSCPxs=
This error usually occurs after a session expires or a user logs out.
 
Information:

<endpoint address="https://test.salesforce.com/services/Soap/c/28.0/0DFw00000000ePf" binding="basicHttpBinding" bindingConfiguration="SoapBinding"
        contract="Salesforce.Soap" name="Soap"/>
      <endpoint address="https://cs17.salesforce.com/services/Soap/class/SpiderProductImportWebservice" binding="basicHttpBinding"
        bindingConfiguration="SpiderProductImportWebserviceBinding" contract="SalesforceProductsList.SpiderProductImportWebservicePortType"
        name="SpiderProductImportWebservice"/>
      <endpoint address="https://cs17.salesforce.com/services/Soap/class/SpiderContractPriceImportWebservice" binding="basicHttpBinding"
        bindingConfiguration="SpiderProductImportWebserviceBinding" contract="SalesforceContractPricesList.SpiderContractPriceImportWebservicePortType"
        name="SpiderContractPriceImportWebservice"/>

Kind regards,
Faizan

Hi,

Because of SSLv3 Poodle vulnerability, we have turned off SSLv3 support on our web server. This in term is causing Salesforce outbound messaging to fail.

Is there a work around with this from Salesforce end?

The outbound messaging processing issue was resolved once we turn SSLv3 back on our web server.

Ted Tsung