Hello Patrick,
the batch response says that field wnd[0]/usr/txtRV45A-TXT_AUART could not be written because it is read-only. If that is the case (sometimes the error texts are misleading or plain wrong), it will never work. Why don't you cut your script short to:
session.findById("wnd[0]/tbar[0]/okcd").text = "/nva01";
session.findById("wnd[0]/tbar[0]/btn[0]").press();
Run this script and see if a) field wnd[0]/usr/txtRV45A-TXT_AUART is visible and b) is writable.
Another thing that springs to mind is: If you use a script that navigates away from the current screen (as your script does) and it's attached to a standard control e.g. a standard button, then the script MUST end with:
return true;
This is documented in Available Events in Scripting - SP02 - SAP Imagineering - SCN Wiki in the details for event GuiButton.onClick.
Best Regards,
Clemens