LONDON.- A rare, hand written pre-production storyboard for one of Alfred Hitchcocks most problematic films, Stage Fright, of 1950 is for sale at the Bonhams Printed Books and Manuscripts sale in London on 7 June. It is estimated at £20,000-30,000. The production files for all Hitchcocks films after 1940 are kept in the Hitchcock archives in Beverly Hills making this the only example ever to have come on the open market. Stage Frightbecame notorious because of a false flashback sequence which Hitchcock later described as one of the two biggest misjudgements of his career. Despite a star led cast by Marlene Dietrich, Jane Wyman, Michael Wilding, Richard Todd and Sybil Thorndike it was not a success though it has undergone critical reassessment in recent years.