When the customer’s try to migrate the project from BW 5.x (which is using the salesforce plugin 2.x) to BW 6.x and if they are using the SalesforceSubscriber activity in their project so they will see the below error when they would try to run the project in BW 6.x studio even if the test connection in the Salesforce Connection resource is successful:- 
 
<CausedBy> java.util.concurrent.ExecutionException: java.net.ConnectException: Cannot connect [https://ap15.salesforce.com/cometd/35.0] : {exception=org.eclipse.jetty.client.HttpResponseException: HTTP protocol violation: Authentication challenge without WWW-Authenticate header, message={ext={replay=true}, supportedConnectionTypes=[long-polling], channel=/meta/handshake, id=1, version=1.0}, connectionType=long-polling}.

<CausedBy> java.net.ConnectException: Cannot connect [https://ap15.salesforce.com/cometd/35.0] : {exception=org.eclipse.jetty.client.HttpResponseException: HTTP protocol violation: Authentication challenge without WWW-Authenticate header, message={ext={replay=true}, supportedConnectionTypes=[long-polling], channel=/meta/handshake, id=1, version=1.0}, connectionType=long-polling}
 

Subscriber failed to login for reason [java.net.ConnectException: Cannot connect [https://ap15.salesforce.com/cometd/35.0]

OS: ALL

As a solution to this problem the customer must change the WSDL number in the Server URL in the Salesforce Connection resource to the latest version which is available and try to run the project again. 

For Example- 

If the customer has migrated the project from BW 5.x which consists of WSDL number 35.0 in the Server URL in the Salesforce Connection resource so they should change the version to 42.0 or which is available latest when you are migrating the project.