It's a ProfileDesign problem. It crash with ProfileComments installed or not.
Quick fix:
Open profiledesign.php and find in line 208:
$lang->load("profiledesigns");
Add below:
if(!empty($mybb->input['uid']))
{
$uid = intval($mybb->input['uid']);
}
elseif($mybb->user['uid'] == 0)
{
error($lang->error_nomember);
}
else
{
$uid = $mybb->user['uid'];
}
Find:
$query = $db->simple_select("users", "profilebordercolor,profilebordertyp,profilebordersize,profilebg,profileimage,profileimagerepeat,theadbg,theadcolor,trow1bg,trow1color,trow2bg,trow2color,tborderbg,tborderborder,tborderbordertype,tborderbordersize", "uid= ".$_GET['uid']."", array('order_by' => 'uid', 'order_dir' => 'DESC', 'limit' => '1'));
Replace with:
$query = $db->simple_select("users", "profilebordercolor,profilebordertyp,profilebordersize,profilebg,profileimage,profileimagerepeat,theadbg,theadcolor,trow1bg,trow1color,trow2bg,trow2color,tborderbg,tborderborder,tborderbordertype,tborderbordersize", "uid= ".$uid."", array('order_by' => 'uid', 'order_dir' => 'DESC', 'limit' => '1'));