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I haven't seen this error from anyone else, but Drupal logged the following when I tried to clone an FCKEditor role:
preg_match_all() [function.preg-match-all]: Compilation failed: unrecognized character after (?< at offset 4 in /.../sites/all/modules/fckeditor/fckeditor.admin.inc on line 253.
We're running PHP 5.1.6. I've never used preg_match_all, but I did a little searching and it looked like a parameter name (?) was missing from the $pat definition, so I thought I'd pass it along.
$pat = "/^(?<name>.*?)_(?<n>[0-9]*)$/"
$pat = "/^(?P<name>.*?)_(?P<n>[0-9]*)$/"
and that seemed to fix the problem