WebService affected by URL

[michael.t.murphy]

I'm making some changes to a web application that has been working
fine for months. It's an intranet app using WebServices along with
AJAX calls. I have a search page with a few dropdowns and a "keyword"
text box that decided to "break" for no reason (I haven't touched the
code on this page in months). If I try to run a search with no keyword
entered in the text box (which has always worked fine) the webservice
it calls generates a "missing parameter" error.

Now for the weird part. If instead of using "http://localhost" I
instead use "http://machinename" I get no error. Same machine, same
instance of IIS, same AJAX code calling the same exact webservice, but
not using localhost makes the error go away. I've searched high and
low and can't find a reason for this behavior.

I know it's probably something stupid but I'm at a loss to explain the
behavior.