Error "401 Unauthorized" calling wshandler service

[Mike Pokraka]

Greetings,
On a 620 system I'm trying to complete a webservice workitem via the
wshandler service using CL_SWF_IFS_WS_EXPORT=>LAUNCH_CALLBACK.
It fails with cx_swf_ws_http_exception after getting a response 401 -
"Unauthorized".

WF_HANDCUST is setup, I checked SICF, the service is set for anonymous
logon. Authorization is correct, since it's being called inside an
authenticated session from a BSP (checked SU53 just to be sure). The URL
is also correct as it works if I paste it straight from the debugger into
a browser - it works and completes the item. I've tried both http GET and
POST methods. I've pulled a couple of hairs out but that had no effect
whatsoever.

Any ideas of what else might be wrong would be greatly appreciated...
Cheers,
Mike

(Crossposted on WUG and SDN BPM & BSP Forums)