IIS 5.1: 403.9 - Access Forbidden: Too many users are connected
I found this blog
that addresses my concern in IIS 5.1 for Windows XP. I recently discovered that it is crippled in such a way that it only allows 10 concurrent connections. Moreover, it is hardcoded to be configured to at most 40. If the maximum concurrent connections have been reached, your website's users will receive the following error:
HTTP 403.9 - Access Forbidden: Too many users are connected
The workaround involves modifying the maximum allowable connections to 40. Still, you're stuck at 40.
Read the complete post at http://alexrazon.blogspot.com/2007/01/iis-51-4039-access-forbidden-too-many.html