This is probably a Photoshop bug but I've tried multiple versions plus the latest snapshot. They all crash photoshop as soon as I select Mono Sans as the font. This is with Photoshop 10.0.1
Can Someone Fix This Bug!
Sorry, but simply not possible with the information at hand. Furthermore if you'd google for "photoshop cs3 font crash" you would see that this seems to be a general problem with Photoshop using a plethora of different fonts, whereas other applications work just fine.
However if you do have any additional information, possibly pointing to an issue in Sans Mono, let us know and we'll do what we can.