You know when this happens???.....sucks right??. You ever CRAVED for FURTHER EXPLANATION regarding this matter??? NO?!? Well, I did...
....because I'm a geek. So here's the first search result my dear old friend, Google, returned...
**warning: little geek talk ahead...feel free to stop reading from here :D**
ok so about the Youtube prompt. Well, obviously the owners of the video has set it in specific countries or region for various reasons, so if your IP address falls outside those countries you will get the "not available in your country" error. Now, I won't be discussing about IP address here but as the name suggests, it's something that identifies a network location. You could read more about IP Address at my other friend Wiki.
I have a way to bypass this however I don't know a Youtube video that may be blocked for the same reason right now. And its pretty late for a guessing game so I can't show it to you right now....some other day perhaps;)