The Classic Pack updated to version 2.5.1
Fixes broken skins due to Mojang not supporting older versions.
This is a client side update, does not affect servers and is not required to play.
Type in the modpack name (The Classic Pack) or paste the following url into the search box.
Finally, click Install at the bottom right of the launcher after you select The Classic Pack from the list on the left. The launcher will handle everything else!