HTTP 405 - Resource not allowed

[Idee]

Hi
I have a website running on ColdFusion and MySql. The site works fine if I give url like

http://myserver/sitename/index.cfm

but if give the url as

http://myserver/sitename/,

the homepage is displayed but any other funtionality does not work e.g from homepage I am trying to add an item to my cart, it give error

HTTP 405-Resource not allowed
Internet Information Services

When I add to the cart, the form which is submitted has action blank like
<form action=&quot;&quot; name=&quot;frm7&quot; method=&quot;post&quot;>

This form works fine if the url is

http://myserver/sitename/index.cfm

Any clues or any help is much appreciated.

Thanks a lot