Lync client on Windows XP Sp3 doesn’t authenticate with Lync server Edge (Remote users). Windows 7 able to support NTLM Authenticate but Windows XP does not support 128-Bit encryption. So that we will do following.
You have to remove Mark "Require 128-bit Encryption".
Guide: Run secpol.msc on Lync Front End server.
Select Local Policies then Security Options
Guide: Run secpol.msc on Lync Front End server.
Select Local Policies then Security Options
Set the following values to "No Minimum."
Network Security: Minimum session security for NTLM SSP based (including secure RPC
Network Security: Minimum session security for NTLM SSP based (including secure RPC) servers
Supported Threads: http://social.technet.microsoft.com/Forums/en-US/ocsclients/thread/7dc73306-c365-4785-b712-6e9d38664d1a
