unable to install Google's Droid Sans Mono font

I've downloaded Droid Sans, Droid Serif, and Droid Sans Mono fonts from google.com/fonts and the first two have installed just fine. Unfortunately, I can't get Droid Sans Mono to install; it looks like some message boxes pop up very quickly, but I can't read what they say. When I validate the font file, it looks okay, but installation doesn't do anything.

Any idea what I might be doing wrong?