Hi Shivaram,
Yes I tried all the solutions mentioned in above link but issue didn't resolved. We are upgrading to Win 7 from Win XP. So everyone is getting new machines & new OS image.
These 20 machines are brand new with Win 7 image. We are accessing QC for the first time on these machine & facing this issue. Eventually this image will be roll out to all users in the organization in coming months & so it will be a bigger problem then.
However QC is working fine on current XP machines without any issue. So it seems there is no issue with respect to dll on server.
Unfortunately we can't disable antivirus on these machines since it is against company policy. Already requested concerned team & they refused.
Still not able to figure out the issue.