Thought we had narrowed it down as to what was causing the white screen before but it seems different now. The only way I can think of doing this remotely is to keep moving up the 3 lines line by line. The sequence of code is as follows:
First, this line in tiki-socialnetworks.php (around line 57):
So the first step would be to put the 3 lines ahead of that line.
The next key point is this line in lib/socialnetworks.php within the function facebookLoginPre() (a little below where we've been working, close to line 300):
$access_token = $this->getFacebookAccessToken();
This would be the next line to put the 3 lines ahead of if the first one doesn't result in a white screen. If this one doesn't cause a white screen, then would put the 3 lines directly after line 193 in lib/socialnetworks.php, which should have the following:
Would move the 3 lines down line by line until you get the white screen.