Bad Request (Request Header Too Long)

Hi all, we have a problem when setting up URL monitoring with OpManager. Essentially when we test the URL ( a simple http://www.blah.com/abc) we get back an error - 400: The request could not be understood by the server due to malformed syntax. The client SHOULD NOT repeat the request without modifications : http://www.blah.com/abc

I ran an Ethereal trace from the server and got the following. It seems that the header is massive and IIS is chucking it back. Any ideas ? :

GET /abc/default.asp?a=1& HTTP/1.1
Host: www.blah.com
Connection: Keep-Alive, TE
TE: trailers, deflate, gzip, compress
User-Agent: RPT-HTTPClient/0.3-3E
Pragma: no-cache
Cookie: ASPSESSIONIDASTCRTDS=MPELBCCCDHNMDMGGOHPLGALP; ASPSESSIONIDQQQCTQBQ=KBGBJNOCAOHOCLNNOKMJMBPH; ASPSESSIONIDSQSDQSBQ=BCLJBCOCMPJKFMLGFABMPNEG; ASPSESSIONIDCSSCSTDT=NBMDPAAAKMHFEFGGNNNNPDMH; ASPSESSIONIDAQQCTSCT=BPNNDHBCLCNGLKMDPJPKINHE; ASPSESSIONIDQQQBQTAR=GCGLJGJDOOFOJFOAEFAJJIDM; ASPSESSIONIDSSRBQQBR=EMAHGCGBJMJNJPIEMACEGEIE;
ASPSESSIONIDASTDSTDT=EONJAELCBFLAIELFOMIFBFKJ;
...
( 300+ repeated lines!)
...
ASPSESSIONIDCSTCTRCS=GDFNCLMCNFFBGICGGFACINOL; ASPSESSIONIDQQSDSQAQ=FGHJJDDAJKJHCGGGIGADOPHL; ASPSESSIONIDSSQAQRAQ=GOOHCLACPKEAJENBBNOAHOPF; ASPSESSIONIDQSSBRSAR=KKIBKJHBHJPLNIDPPHBNHKMC; ASPSESSIONIDSSRBSSAR=CMPLJPHDBMNDENFKADBAEKLH; ASPSESSIONIDCSTATTDT=PEKBMIGDAAOGCKENPBMHCMNM; ASPSESSIONIDQQQDQRAQ=EGJLGFAAEKOBDIOOAIEMFDGM; ASPSESSIONIDSQTARTBQ=NOPJJGNCLBBBDNABEBLFAOHL; ASPSESSIONIDQSTDSRAQ=PKINOEECDJLFEPJAJIBJCOFB; ASPSESSIONIDSQTBRSAR=DLPBJGNCMJHGJOHKEPFHHPLB; ASPSESSIONIDQQQBQTBR=FPFFNNKAOJKAENAHGNPNGNFJ; ASPSESSIONIDSSRARSBR=KDHLJMNABAIJNKLEFLNFNFIA
Cookie2: $Version="1"
Accept-Encoding: deflate, gzip, x-gzip, compress, x-compress

HTTP/1.1 400 Bad Request
Content-Type: text/html
Date: Tue, 13 Dec 2005 13:43:57 GMT
Connection: close
Content-Length: 46

<h1>Bad Request (Request Header Too Long)</h1>