Windows or linux?
Run in debug mode (for linux use GDB) and see what the actual crash reason is. That way you know if it's a dead pointer, or whatever. Also if there's an allegro log, read that.
Double verify that font is loaded, pointing to a real font, and that the code you gave us is exactly the code that shows the problem.
Check if a different font works, maybe you have some sort of corrupted font file and Allegro doesn't catch it.
for linux, debugging is as easy as:
[it will crash]
That'll show the function it died in, and what exact line of code it died on.
If you type "list" it'll show ten lines of code around where it crashed.
If it's windows, visual studio (or mingw or whatever) have their debuggers too.