why is my ihttphandler (IIS7 integrared) not being called for some urls

<add name="scep" verb="*" path="scep/*" type="xxxxx"/>

I get called on a GET to

/root/scep/?operation=GetCACert&message=foo

and

/root/scep/?operation=GetCACaps&message=foo

but not

/root/scep/?operation=PKIOperation&message=XXXXX(long base64string)

I set maxQueryStringLength开发者_JAVA技巧 to allow this long URL but I dont get called. IIS returns 404 to the client

seems that there is an upper limit to the length even when max query length set