Strange behavior from TMG 2010

Hi all,

I have a strange issue in accessing internet behind TMG 2010 from random users. Sometimes internet works fine and sometimes not. I have checked the monitor section and I found this alert "Global denied packets rate limit: The number of denied TCP and non-TCP packets per second exceeded the system limit. As a result, Forefront TMG reduced the number of records of denied packets that are written in the log."

I did the following:

1. Increase the number of TCP and non-TCP requests in Flood Mitigation Settings.
2. Add the range of my subnet in the exception section to allow all users.
3. Disable Mitigation flood attacks and worm propagation.

And the warning still exist and it is not directed to certain host.

Thanks in advance.