Win 7 PCs Disconnected From Exchange – Schannel is at issue

Hello,
We are using 8 PCs with Windows 7 and Outlook 2007 in our office. We have also a server running Small Business Server 2003 and Exchange Server 2003.
When we were using old PCs with windows XP and Outlook 2007, we didn’t face any problem during connecting, now with updated system, the condition of Outlook on 3 PCs is as "Disconnected from Microsoft Exchange" displayed once a day.
I have to restart because it fixes the problem for a period but not for long times. I also have used Microsoft Exchange Best Practices Analysis Tool to address a number of issues on the server, but can’t get rid of this problem.
I looked through the application and system event logs to solve these issues, and found the following error during the time of disconnections-
SChannel
The following fatal alert was generated: 10. The internal error state is 10.
– System
– Provider
[Name] Schannel
[Guid] {1F678132-5938-4686-9FDC-C8FF68F15C85}
EventID 36888
Version 0
Level 2
Task 0
Opcode 0
Keywords 0x8000000000000000
– TimeCreated
[SystemTime] 2010-12-16T13:31:38.098155500Z
EventRecordID 4097
Correlation
– Execution
[ProcessID] 532
[ThreadID] 572
Channel System
Computer (****PC Name****)
– Security
[UserID] S-1-5-18
– EventData
AlertDesc 10
ErrorState 10
Any help will be appreciated.
Thanks.
