I recently installed vers 2.1.5 and noticed when I diffed against 2.1.4 that this fix hadn't been merged into the current source, even though you mentioned in the changelog it had been fixed?
"- Fixed problem with transcript deletion"
On line 59, if...
if ($GLOBALS['conf']['opdelete'] === true || admin()){
is replaced by
if ($GLOBALS['conf']['opdelete'] === true || $GLOBALS['auth']->admin()){
that should fix the error.