Cannot find or create the font ArialMT

Just recently I started getting the message when opening pdf files containing ArialMT (typically by PC users) (I am using a Mac obviously and Acrobat 9.3.3):

Cannot find or create the font ArialMT. Some characters may not display or print correctly.

I've looked around in the forums and no one else has had this problem answered. Can't find anything else on the subject that pertains to how to fix it on a Mac, only on a PC using coding.