It means that the area of Excel's memory that is devoted to
font application records is filled up, and apparently there
is no way to make it larger. Sometimes just closing the
workbook and reopening it helps. I've been told that
Excel makes a record of fonts used in each cell as they are
applied. Eventually, this record list must get VERY long
and it is confined to a fixed size area of memory. It
helps to assign a font to as many cells as you can all at
once. For example, if all the cells in a given column will
have the same font, then select all the cells, then make
the font application. The cells supposedly do not have to
be contiguous to make use of this. Just hold down the CTRL
key while you select as many as you can, then apply the
font. Try it. . . it might help.