Safari blocking shut down?

Hi guys,
new to mac's and set up etc, just getting started with macbook pro and the operating system but have had it for a few months now. For some reason in the last few days, i have been unable to shut down the mac successfully. every time I try to do this, a window pops up saying "safari cancelled shut down - please close down safari and try again"

problem is,the safari windows are all closed down, and the option on the safari program tabs itself saying "quit safari" is unable to be chosen! can anyone tell me why this is and how to remedy it?
thanks!

I'm not experienced enough to be able to address the WHY. Sorry :/
However, I have a fair amount if ideas that should remedy it.
Have you tried a software update? If not, this may (possibly) give you the newest version of Safari, which usually involves bug fixes.
Try resetting Safari. This can be done under the "Safari" menu once you open the program.
Have you tried another web browser such as Firefox or Chrome? I highly recommend you try others.
If none of this works, try clearing your cache at the least. Short of a re-install, try hitting Command+Q when you're done with Safari. If that doesn't do the job, you'll just have to force quit (Command+Option+esc).

Hope it all works out!