Does it happens when trying to choose any fonts, or only from certain types of fonts?
For example, can you select a "PS, printer, single-byte" font without error? They don't use the Windows fonts folder, so if they work fine, it may be a problem with the TrueType fonts installed. Do you remember the last font that you have added before it started happening? Maybe one font is causing this issue...
If the "PS, printer, single-byte" doesn't work, then there could be something wrong with the install. I would suggest maybe doing a Repair of PlanetPress, and see if that helps.
Regards,
Raphaël Lalonde Lefebvre