Hello navinkumarpk and welcome to the forum.
I don't think this is a Vista issue , because your error saying ' some SCOT flag missing error' seems more likely a bad installation to me.
If you have indeed all 3 cossacks game's, have a look on your BTW cd rom and try to install the mod from the cd rom, it's the baddog mod. If you still have the problem then, then let me know. If you don't have the problem, then it means something is wrong with the file's on the site and I should have a look in to it.
Also, did you first install the Baddog Mod or first the OC mod? The right order would be to first install the Baddog Mod and then the OC mod and then the OC mod Patch.
If the problem still persists, let me know, and i'll look deeper into it.