This message is generated when the indicated value of the DefaultFont option does not have the expected form.
The value of the DefaultFont option is expected to be a string giving the name of a font, a number giving the size of a font, or a list giving both the name and the size of a font.
The default value of the DefaultFont option is the value of the global variable $DefaultFont.
Off[message] switches off the message; On[message] switches it on. For example: Off[DefaultFont::dfont].