Hi Guys,
I'm experiencing this exact same issue... FusionPro crashing on Avenir Next Regular...
INFO: Using font name "Avenir Next Regular" instead of family name "Avenir Next".
** LogAllLoadedFonts: Located font: AvenirNext-BoldItalic
When opening a template, no fonts are selectable. It's like there are no fonts being loaded to FusionPro. I ran on Mavericks for a week or so with no problem until I had to load fonts and this broke FusionPro's access to all fonts. Same thing.
Running Mavericks with Fusion Pro 9.1.0/Acrobat XI Pro on MacBook Pro 17-inch, Mid 2010 8GB RAM 2.8 GHz Intel Core i7