Please help my friend! My friend recently downloaded the free portal from steam for PC. I played Garry's Mod and decided to gift him Garry's Mod through steam so we could play together. After everything installed, he launched Garry's Mod, but an error came up which said "A Source engine is required to play Mods". I knew that Garry's Mod needed a Source Engine typed Valve game, and according to steam and other people Portal was a Valve game with Source Engine. In fact, a long time ago when Portal was the only Steam game I had, I bought Garry's Mod and it worked well with Portal in Steam. What is going on with my friend's Garry's Mod? I checked other forums addressing both mods and the limited time free portal like me. They all had the same error, and the forums were agreeing that Valve screwed up the Source in Free Portal, making steam not recognize portal as a source engine game. Is there a way to fix this? Please help! Thanks!