Error 'System.CalloutException: Callout loop not allowed'

1. In Org B create a Webservice class AccountPlan  making a callout to another Webservice 
For example Org B is making a Callout to the calculator webservice to add two integers calculator.wsdl attached to the article. 
2. Generate WSDL for class AccountPlan . Call it OrgB.wsdl
3. In Org A, use OrgB.wsdl to create WSDL2Apex Class soapSforceComSchemasClassAccplan
4. Add Org A add https://OrgBInstance.salesforce.com/services/Soap/class/AccountPlan to remote site settings 
5. In Org A create the Rest class CallAccountPlan to initiate the Rest call
 

@RestResource(urlMapping='/createAccountPlan/*')
global with sharing class CallAccountPlan{
    
    @HttpGet
    global static String doGet(){
        soapSforceComSchemasClassAccplan.AccountPlan stub = new soapSforceComSchemasClassAccplan.AccountPlan();
        stub.SessionHeader = new soapSforceComSchemasClassAccplan.SessionHeader_element();
        stub.SessionHeader.sessionId = Session Id;
        return stub.createAccountPlan();
        }
}

6. Make a GET call /services/apexrest/createAccountPlan/ from REST explorer in Workbench
7. We see the error : message: System.CalloutException: Web service callout failed: WebService returned a SOAP Fault: System.CalloutException: Callout loop not allowed