There are two symptoms related to fonts that you may get. That is, your special fonts may not display correctly. This is a common problem with barcode fonts. The other issue, is when exporting to PDF, you get the following message: "Export Error: Selected exporter does not support one of the features used in this report."
Basically, you are not able to see fonts or export to PDF. This is a major issue when you use barcode fonts.
I found that this problem is due to lack of support of some OTF fonts. The solution is to convert the fonts to TTF.