Hi Julian,
Have you set the parameter service\protectedwebmethods=DEFAULT in all the profiles of SAP system?
In all the profiles means , it will include the start , instance and default profile for all the instance name
(SCS , ASCS , DVEBMGS00 , JC , J<xx> ) then you have to maintain the parameter in all the instance,start profile.
If the above parameter does not wok , then repeat the same steps with the below parameter
service\protectedwebmethods=NONE
With Regards
Ashutosh Chaturvedi