I had wrongly updated DVD region code and not able to change it. When inserting local region DVDs, the dialog box to change the Code is not coming up but the file is showing "not permitted". Kindly help!

I have no experience with this issue, just trying to help. According to what I read in the support doc, you should just get the change window again.

http://support.apple.com/kb/ht2397

I'm going to suggest you first try a restart, if you haven't since you made the change the first time. If that doesn't do it, try logging in as a different user and seeing if you can make the change that way. It's a firmware change, so if you do it as a different user name it'll still apply to your normal user when you log back in with that account.

Region encoding is the mechanism that enables motion picture studios to control the worldwide release of their movies. It is required by the DVD Forum (http://www.dvdforum.org/forum.shtml) in all commercial hardware DVD players. Every DVD-Video disc contains one byte of data representing a region code, which limits where the disc can be played.

http://support.apple.com/kb/HT2397

Once you have set the region in DVD Player five times it cannot be changed.

Instead, use VLC to view videos from different regions:

http://www.videolan.org/vlc/download-macosx.html