Originally Posted by The Observer

Yeah.... I no longer have any of my TTT maps, I don't have FLATGRASS ANYMORE, WHEN IT COMES WITH THE GAME, and I lost about 2/3 of my maps. WTF Garry's Mod. Why.

Try verifying the game cache... or If you feel up to it... delete everything and re-download the game... with the recent update... It might be easier just to start over with a clean Gmod copy... lel