If you suspect you have this problem, and are seeing the message "EventID 4226: TCP/IP has reached the security limit imposed on the number of concurrent TCP connect attempts" in your Event Viewer, in order to rectify this problem you will need to run a small program that will allow you to change the connection attempt limit to a higher number. It is available at www.lvllord.de.
Run this program and increase the maximum number of connections from 10. A maximum setting of 50 connections might be a good place to start but you may need to go even higher to get the best performance from slsk.
Be careful when you run this patch! It changes important system settings and if done incorrectly could cause you major problems. USE AT YOUR OWN RISK!
The same thing can happen to you if you are using Windows Vista. The best way to get rid of this limitation in Vista is to install service pack 2 through Windows update, because Microsoft removed the limitation in in SP2. The limitation is also removed from Windows 2008 SP2 and Windows 7.
A patch that works for all operating systems since XP sp2 is available here.
It must be applied again after Microsoft hotfix or service pack modifies tcpip.sys.
Another possibility is not patching the tcpip.sys file but patching it in memory after it loaded (you can run the memory patcher once (thus needing to apply it again after reboot) or by installing a driver that does it automatically after booting). More info here or here.
Both can also be downloaded from Softpedia, Half-open and TCP-Z.
Again, use at your own risk.
Edited by Chiquitin, 20 June 2009 - 01:51 PM.