I’m having this same issue. The Preview is not “previewing” and in characters it says “font not available”. What am I missing?
From where did you download MainType, and which version are you using?
The current release version is 7.0 build 1032. Check in Help, About, and Check for Updates.
From the high-logic website. I’ve attached a screen shot.
Is the Eye icon enabled?
You seem to have a lot of fonts with errors (the blue icons) but the green one is installed.
Have you checked for font errors from the Tools menu?
Maybe I’m just too new to know what i’m doing! 
Now those in a red state are previewing but nothing in green
You don’t have a lot of fonts in your library. I suggest uninstalling MainType, deleting all of the databases, then reinstall and remake your groups and tags.
We are very sorry about the inconvenience.
We’ve had a couple of customers with the same issue, so it seems like a bug to me. There is one customer who is currently working with us to locate and fix the issue. If that doesn’t help, we’ll contact you to see if we can mutually solve the issue.