The font is not installed on this computer
This message occurs if you try to select a font which is not installed on your computer, from within the special fonts manager. The list of font tables displayed in the special fonts manager are tables shared by all Q++ users, while actual fonts must be installed on each PC separately.
If this message refers to a font which is no longer used by any of the users at your site, then you have the option of clicking YES to have Q++ delete the font table associated with this font. But you should only do so if the font is not used anymore by any other user.