IF YOU UPDATED YOUR MINECRAFT AND YOU HAVE A BUKKIT SERVER YOU WILL NOT BE ABLE TO JOIN OR PLAY ON YOUR SERVER SO DOWNLOAD THIS AND FOLLOW THE INSTRUCTIONS BELOW:

STEP 1: DOWNLOAD ME:-removed-

STEP 2: GO TO START AND TYPE IN %APPDATA%

STEP 3:THEN CLICK ON .MINECRAFT AND GO INTO THE BIN FOLDER

STEP 4: REPLACE THE OLD MINECRAFT.JAR WITH THE NEW ONE YOU DOWNLOADED.

STEP 5:NOW LOAD UP MINECRAFT AND JOIN PEOPLES GAMES OR GO ON YOUR SERVER!

HOPE I HELPED THANKS!

ZaphodX:
Navigate to your .minecraft/bin folder
Rename 'minecraft-1.0.0.jar' to minecraft.jar