File this one under the "yet another useless error" category. I was trying to publish a form that I prevously had succesfully published to my development VPC. Every time I tried to publish it would say "the following url is not valid" when I entered the path to the sharepoint site.
Doing the standard search for the error yielded several potential solutions ranging from re-installing .NET, make sure there's a site at the root "/" and make sure there's a SSP.
Additional searching yielded the other option of stopping the "System Event Notification" Check out this blog entry.
Don't you just love obscure error messages?