IIS on Windows XP has a default concurrent connection limit of 10 for the root website. Any connections made after 10 connections are being used up are greeted with a HTTP 403.9 Access Forbidden: Too many users are connected error message.
The default connection limit can be changed to the absolute maximum of 40 concurrent connections using the IIS adsutil.vbs administration script:
First you need to set the default windows script host to be the console. Do this by running the following command:
cscript //h:cscript
Next run the adsutil.vbs script from the Inetpub\AdminScripts like so:
C:\Inetpub\AdminScripts\adsutil set w3svc/MaxConnections 40
Job done!