In orderBy66 there is a reference to $count, which appears not to be in scope.

       declare default element namespace "http://www.w3.org/XQueryTestOrderBy";

       <results>{
           for $i in 1 to 100
           order by -$i
           let $c := count
           let $e := <e i="{$i}" pos="{$count}"/>
           order by number($e/@i)
           where $count gt 90
           return $e!@pos!number()
           }
       </results>