Android : How do I get the profile picture having a user id from the friends picker?

I'm using the friends picker and obtain the selected user id. It's something like this : AaLO4uyQLCrltBKryBnaTppP1ThNTREseQYV796H5JyPviztByQkST7Z362i7YIEYi2ZGcvX4shtFnXR0dd0g0yFwwRLt6SFTasdqNB19UtcvA

Then, I'm trying to obtain the user's public information and it's profile picture, but both requests return : { "error": { "message": "(#803) Some of the aliases you requested do not exist: AaLO4uyQLCrltBKryBnaTppP1ThNTREseQYV796H5JyPviztByQkST7Z362i7YIEYi2ZGcvX4shtFnXR0dd0g0yFwwRLt6SFTasdqNB19UtcvA", "type": "OAuthException", "code": 803 } }

I tested both in Graph API Explorer (https://developers.facebook.com/tools/explorer/145634995501895/?method=GET&path=AaLO4uyQLCrltBKryBnaTppP1ThNTREseQYV796H5JyPviztByQkST7Z362i7YIEYi2ZGcvX4shtFnXR0dd0g0yFwwRLt6SFTasdqNB19UtcvA%2Fpicture%3Fredirect%3Dfalse&version=v2.1)

and the url in the browser : http://graph.facebook.com/v2.1/AaLO4uyQLCrltBKryBnaTppP1ThNTREseQYV796H5JyPviztByQkST7Z362i7YIEYi2ZGcvX4shtFnXR0dd0g0yFwwRLt6SFTasdqNB19UtcvA/picture?type=large

Simply it does not work. Is there a difference between the user id returned by the friends picker fragment, and the facebook id? I'm asking this because the id returned by the /me query is much shorter : "id": "777840545588528"

Can anyone help me? What am I missing?

Many thanks!