Why I am getting delays when accessing my configured sources in a Muse Proxy Application running on Windows Server?

This may be due to the default Windows limitations for network connections, more exactly the max limit set on simultaneous network connections. Receiving the TCP/IP has reached the security limit imposed on the number of concurrent TCP connect attempts error in Windows Event Viewer for Event ID 4226 is a clear sign of reaching the limit set on simultaneous network connections.
To disable the TCP connections limit follow the steps:
1) Click Start, type regedit in the Start Search box, and then click regedit.exe in the Programs list. If you are prompted for an administrator password or for confirmation, type your password, or click Continue.
2) Locate and then double-click the following registry key:
3) In the Value data box, type 0, and then click OK.
4) Exit Registry Editor.
5) Restart the computer.

If the EnableConnectionRateLimiting registry entry does not exist it must be added.

The Microsoft Knowledge Base article KB969710 confirms that the half-open TCP connections limit is disabled in Windows Server 2008 with Service Pack 2 (SP2) and in Windows Vista with Service Pack 2 (SP2).