Font works in windows but partially in mac

I have a font I have sold successfully in Windows for 4-5 years, however mac users have problems. The last comment was the font lost the bottom half of the characters when used. Can you think of where I look to correct this. I have got a bit rusty so make it fairly detailed if you give any suggestions please.
Anne Hext :question: :confused:

Format, Settings, Metrics, Maximum, Calculate should fix such problems.