I have another error that causes my whole computer to crash, but I found a way to get around it AND still play the game. So, first try reinstalling. If you can play it the first time, but not any other time, then this will most probably fix your problem. So verify that reinstalling the game causes the game to play. Then after every time you hit play, it crashes. Here are my steps:
1) Reinstall the game fully. DO NOT PLAY IT YET
2) Verify, just in case.
3) Copy the files:
-common/portal 2
-portal 2 client binaries.ncf
-portal 2 common.ncf
-portal 2 win content.ncf
-sourceinit.gcf
-winui.gcf
and place it into a different folder (I made the folder steamapps2)
4) Delete all those files in your steam apps folder.
5) Copy the files from Steamapps2 into your Steamapps folder. Depending on your transfer speed, it should take roughly 10 minutes (Thats how long it takes for me).
6) Play the game. Then immemorially after exiting the game, repeat the steps so the next time you wan to play, it'll be ready.
Although it takes 10 minutes, it sure is a hell-of-a-lot faster than reinstalling and downloading the whole game.
