Also we have checked server IP and Port settings, all are looks good. In fact server is running with these setting quite a while now and this issue occurred all...

No, registry setting not enabled yet. I am not fully convinced with this work around yet. Are we sure enabling this setting would not cause any issue, are there any...

Thanks for the reply SanDroid, but making these registry changes has been already suggested in the article

http://support.microsoft.com/kb/2491214

But it is applicable for SQL 2008 R2, where it also suggest to...