"failed to open document" I got this message

each time I try to open a flash movie , flash keeps giving me this message " failes to open this document "
I wonder why it happens with some movies and it does not with other
Please help me ,
thanks much

if you are running Flash 5 and you attempt to open a Flash MX document you will get an error like that, make sure they are all the same format.

I am trying to open a Flash 5 movie from Flash 5 , the movie was a tutorial that I got from our class website , I assumed that it was a mac file that I am trying to open from my PC , did anyone encountered this kind of problem?