Cant access msmdpump.dll setup in IIS from a box other than localhost

I configured access to SQL Analysis Services via IIS on one of my machines, as per the following instructions:

http://mglaser.bloggingabout.net/2008/08/15/configuring-http-access-to-sql-server-2008-analysis-services-on-microsoft-windows-server-2008/

I tested using Excel on the same machine and it works fine. I access using the following url (I can access without using localhost on that machine):

http://10.3.29.79/OLAP/msmdpump.dll

But when I try it from any other machine on the same network using Excel it does not work. Now I know you cant use IE for testing but I just watned to see if I could resolve to even the error you normally get in IE.  Something along the lines of:

- <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
- <soap:Body>
- <soap:Fault xmlns="http://schemas.xmlsoap.org/soap/envelope/"><faultcode>XMLAnalysisError.0xc10e0002</faultcode><faultstring>Parser: The syntax for 'GET' is incorrect.</faultstring>
- <detail><Warning WarningCode="1090584599" Description="The 'Invariant Language' locale for UI is not supported." Source="Unknown" HelpFile="" /><Error ErrorCode="3238920194" Description="Parser: The syntax for 'GET' is incorrect." Source="Unknown" HelpFile="" /></detail></soap:Fault></soap:Body></soap:Envelope>

But all I get when I access from other machines is an error 500, internal server error.  I'm not worried about it not working in IE as I know it cant, but I do think there's an issue accessing from any box except the host. 

Thanks for any advice!