WAS plugin gets error reading server variable SERVER_PROTOCOL

[Too Many Late Nights]

I'm using IIS6 on Win2k3 to authenticate users. In IIS we run the WAS
plugin (v5) to decide whether or not a request needs to be forwarded to
our domino server (v7.0.2) to be handled. (the configuration worked
when we used Win2k, IIS6,WAS5,Domino6.5.4)

Now I get the error shown below in the plugins logging. As I
understand, the SERVER_PROTOCOL server variable should contain HTTP/1.1
(so I dont understand why the expected length is 32). I have tried
using Fiddler tool to see what the value of the server variable has but
I cant see any server variables at all.
Does anyone know whats wrong? Does anyone have a solution? Does anyone
have a list of the esiResponsePassThru rc codes?

thanks
Extract from logging:

TRACE: lib_stream: flushStream: Flushing the stream
TRACE: ws_common: websphereExecute: Wrote the request; reading the
response
TRACE: lib_htresponse: htresponseRead: Reading the response:
TRACE: HTTP/1.1 302 Found
TRACE: Date: Mon, 04 Dec 2006 14:13:45 GMT
TRACE: Connection: close
TRACE: Location: <changed to protect the
innocent>/OpenDatabase&login
TRACE: ws_common: websphereExecute: Read the response; breaking out of
loop
TRACE: ws_common: websphereExecute: Done with Request to app server
processing
TRACE: ESI: esiControlCreate: no Surrogate-Control header found
TRACE: ESI: esiResponseGet: bypassing ESI
TRACE: ESI: esiResponsePassThru
TRACE: iis_plugin: cb_write_headers: In the write headers callback
TRACE: iis_plugin: getServerVariable: Getting server variable:
SERVER_PROTOCOL
TRACE: lib_htresponse: htresponseGetContentBlock: Getting the next
content block
TRACE: lib_htresponse: htresponseGetContentBlock: Read -1; not expected
length of 32
TRACE: iis_plugin: cb_write_body: In the write body callback
TRACE: iis_plugin: cb_write_body: Writing chunk
WARNING: iis_plugin: cb_write_body: Response write failed, OS err:
10054
ERROR: ESI: esiResponsePassThru: failed to write body: rc = 7
ERROR: ESI: esiHandleRequest: failed to write response
TRACE: ESI: esiUrlDestroy: '/'