Context.RewritePath() no longer working..

I'm using the Context.RewritePath() method in my Global.asax file under the Application_BeginRequest method, and it works fine on my home computer, but when I upload it to my dedicated server, it no longer seems to work. It just gives me a 404 error.

I'm basically taking this url: www.mydomain.com/mystore

and redirecting to something like this: www.mydomain.com/stores/default.aspx?storename=mystore

could it be something with IIS, since my url doesn't end with .aspx? if so, how do i fix that? what would i change in IIS?

Thanks!
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