I did everything on this page http://forums.xbox.com/xbox_forums/xbox_support/f/8/t/25.aspx still can't play it.
Here are the answers to the questions page asked:
What game are you trying to play? GTA: San Andreas
Is it a disc or downloaded version? Downloaded
What type of console are you using? Xbox 360 Slim 4gb, with a bought separately 250gb hard drive
What size HDD are you using? 250gb
What error code or message are you receiving? Game Error: Can't play the game, try downloading it again (something like that).