(UPDATED 2 MARCH)
You might have noticed the mod has stopped working since the recent Half-Life 2 update.
There is an easy fix, which you can download here: (UPDATE: The fix was not as easy as I thought at first, but I think this time it will work.)
NOTE: The fix requires that you have the Source SDK base 2013 installed and switched into the "upcoming" beta on the betas tab. It also requires that you have Half-Life 2 in the same steam library as the mod and the sdk base. (Which you probably already do, if you have other mods working). ALSO, you need to opt OUT of beta programs for Half-Life 2 now. The install guide says to opt in, but it's out of date now. So to be clear:
Source SDK Base 2013 Single player - needs to be in 'upcoming' beta,
Half-Life 2 - needs to be opted out of all beta programs.
Thanks to BloodyBody for bringing it to my attention, and to Gunship Mark and the MMod team for a working example of gameinfo.txt.
