font missing in one file only

I have installed and activated the font (using FontExplorer X Pro), and the font shows up in the font menu. But when I select it I get the square brackets and the default font instead.

When I opened a new blank test file, the font worked just fine, so for some reason it is "missing" only in my working file.

Does anybody know how to fix this, or what is causing it?

I'm using InDesign CC 2014 on a Mac OSX 10.9.4, all software is up to date.

Thanks.