With the game's first DLC release now fixed for Xbox 360, all platforms are finally able to access the online modes of PES 2014.
Although an official statement has yet to be made, I can confirm Data Pack 1 has indeed been fixed. Since Friday evening, many members of the community have managed to download the pack without receiving any error messages during the installation process.
If it doesn't work for you straight away, just hit download once more and try again. The progress bar should reach 100% after two or three attempts.
To download Data Pack 1, simply go to the main menu, scroll left to Statistics and then select Data Pack Update.
DP1 unlocks all basic online game modes - including Master League Online - as well as adding official matchballs for the top leagues of Argentina and Chile.
UPDATE (Thursday 24rd October): Xbox 360 users can download Patch 1.03. The new update fixes online issues and adds Master League Online: