I tried both. But there is no change the way it responds when content doesn't match with extension. I think associations are ok since I can open files by double clicking when the content matches with extension. Is there any way to bypass the step(checking of content vs extension)? Thanks for your continuous support.

Sure, it's all open source. Download the Nautilus source and remove that check. Re-compile and replace Nautilus in the system directory.

However, as I said, I don't have the problem and I'm running FC6 with current maintenance. It's likely something else is causing your issue.

I am not that good in programming. So I think I can just use right click. Anyhow my machine got updated in this. Thanks for your continuous help.