When I unlock an achievement on MS online games and go to post it on Facebook it is block...

You would have to talk to them about changing their policies.

I would like to add onto this thread as I, too, am experiencing the same issue with posting to Facebook and receiving the same error code: 0x838107D2

All permissions have been given, cache has been cleared multiple times, revoked and added social sharing...and the conclusion I've come to is that the issue is solely within the game.

The issue with Pac Man CE DX+ is that a particular game unlock requires that you earn a set of 'medals' from posting achievements to Facebook. I am able to post achievements to FaceBook if I am just in the Xbox Dashboard. If I'm in game and i hit "X" to
go to the menu I can also post achievements to FaceBook. It's only when I use the In game posting screen in Pac Man CE DX+ and try to post to Facebook that way that I get the error. Unfortunately, using the ingame posting screen is the only way to achieve
the medal.

hope that helps!

Where you online at the time when a achievement post unlocked?

Hopefully they dont block singleplayer games but they could just block online play for pre- owned discs.I could see having to pay 80 ms points for an hour of online play or $10 for an unlimited pass.Not saying I like it but microtransactions are our future.Look
at Farmville on Facebook and the many other free games that sell coin packs for in game items.I found all those free ios games are not free.And blocking people from online games hurts everyone.It makes MS and the game publishers look bad and new and used disc
owners mad.

Are you online while unlocking these achievement,you have to keep all save files for the game to unlock the achievements if going offline to online. Ive lost achievments from being offline then going online. So make sure your save file is there and your
online