It's possible your iPhoto Library has problems beyond the Rebuild function's ability to repair. An alternative could be to back up*
the Library and rebuild it with iPhoto Library Manager**
. iLM's approach actually recreates the Library using iPhoto's albumdata.xml file, and may yield a properly working Library, albeit without items like slideshows, books or calendars, but with albums and keywords, faces etc.*
iLM doesn't overwrite iPhoto's original Library, but any operation with the latter warrants a backup.**
) Fat Cat's iLM page mentions a trial download, but doesn't specify limitations.