Excel 2007 : "Data Source Not Found" when refreshing .xml source from web site

I am having some trouble with a mapped .xml data source. I'm trying to set up an external source so that I can distribute a template to some vendors and have them refresh data down the road. I've mapped five tables as an XML data map and all works perfectly as long as the data source is on our internal network. Obviously, since I intend to send this outside the company, that won't help me with the final product.

Unfortunately, the only place I have where I can publish the files will require users to log in with a username and password. (Neither is sensitive and can be saved with the template in clear text.) I have successfully mapped the data from the website (using the Data -> Import XML menu option.) I can also refresh the data from the website up until the time that I close Excel.

I can close and reopen the file, but if I close Excel completely I get an error message the next time I attempt to refresh the data. If I then re-import the data for any one of the tables (which provides me with a password prompt), I can refresh the data for all of them.

Any suggestions for how I might retain the password in the XML data source definition? Or trick Excel into entering the password for me? (I have tried the obvious one of picking the "remember password" option and have also tried logging into the website manually before doing the refresh.) I'd prefer not to have to remap the data every time I do a refresh...

Cheers and thanks in advance,
Corey

Sample workbook attached demonstrating the issue... Boiled down to just one table (only has 3 lines as proof of concept). Right click in the table and choose "XML -> Refresh XML Data" to see the error.

Cheers,
Corey