BuddyPress.org

Go to Settings -> Miscellaneous Settings
.

Set “Store uploads in this folder” to “wp-content/uploads”.


Set “Full URL path to files” to the REAL FULL PATH of your uploads.


Then change “bp-core-avatars.php” line 389:

Replace:


if ( !$path = get_option( 'upload_path' ) )


$path = WP_CONTENT_DIR . '/uploads';


With:
if ( !$path = get_option( ‘upload_path’ ) )


$path = WP_CONTENT_DIR . '/uploads';


else
$path = ABSPATH . $path;

It fixes the problem.

Source: https://buddypress.org/forums/topic/avatar-upload-issues/page/2

This is really something that need be fixed with the next release.