I got this issue resolved. I was using MC ID/PWD which is something workflow does not expect. I used my own ID/Password (administrator) and it worked. Thanks for all your help.

thanks cjpicc1 for reply.PFB the payload. <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:urn="urn:xtk:workflow">   <soapenv:Header/>   <soapenv:Body>      <urn:Start>         <urn:sessiontoken>id/password</urn:sessiontoken>         <urn:strWorkflowId>1171720</urn:s...