Windows XP, by design, only allows a limited number of connections. The number is ten. If you need more, you're supposed to buy Windows Server.
See
Inbound connections limit in Windows XP[
^]
The following may or may not help:
1. You could try lowering the
KeepAliveTimeout
value. See
How to change the default keep-alive time-out value in Internet Explorer[
^]. That may or may not help and is certainly not a long term solution for an active web site.
2. You could try lowering the
TcpTimedWaitDelay
value. See
Avoiding TCP/IP Port Exhaustion[
^]. That may or may not help and is certainly not a long term solution for an active web site.