Hi,
For the issue: " run time viewer shows an error saying there was a save conflict due to which the updating did not happen." I would suggest you to disable run time viewer during replay and check in the replay log if the error message appears.
The fact that errors can appear in the Run-Time Viewer that do not necessarily indicate script level problems.
http://support.openview.hp.com/selfsolve/document/KM171870
For the issue with the Authentication header that is not available in any of the previous server responses if it is generated at the client side, unfortunately the option is to write a customer code which simulates the algorithm for its generation.
Kind regards,