"Replaced missing AutoCAD SHX Font ISO"
Further details from Message Center include:
"Replaced missing AutoCAD SHX Font ISO with default AutoCAD font msdefault. Some text may not display correctly. Make sure that the SHX font is present in the AutoCAD fonts directory or MS_DWGFONTPATH contains the path to the location of the SHX font."
One option to try:
Fonts in MicroStation