Diffferent results from standalone than with IIS

Tomcat v 3.2.1 and IIS 4.0

I am using form based authentication for url-pattern "/sales/*". Whenever I
try to access files under this protected URL I am prompted with the login
page "/security/login.jsp". However, when I try to login I get the following
405 error, and the resulting URL in the location bar is :
http://localhost/security/j_security_check. If I run this in standalone
Tomcat everything works fine. Why doesn't it work correctly when integrated with IIS?

HTTP Error 405

405 Method Not Allowed
The method specified in the Request Line is not allowed for the resource
identified by the request. Please ensure that you have the proper MIME type
set up for the resource you are requesting.
Please contact the server's administrator if this problem persists.

What do I need to do to get it to work correctly with IIS?

Thanks in advance,

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