Which font is it? Where did you get that font?
I know that I downloaded some free fonts at DaFont and some just won’t work, no matter what. One even made one of my layout documents crash and refuse to print: once I changed the font to another typeface, all was good again. So basically what I am saying is that some free fonts out there are total junk. 
And 190+ fonts is kinda beefy for Font Book, I find. Try FontExplorer X (explained in my earlier post above, just be careful the version you download though) and it might allow you to import that font after all.
It has happened on a couple of occasions that Font Book would refuse to import a font and that was one of the reasons why I decided to use FontExplorer X a couple of years ago just to see if the font would work and it did.