[otrs] can't open developer doc

Dear All, I can not open this document, may I ask who has the same problem with me? ftp://ftp.otrs.org/pub/otrs/doc/doc-developer/2.4/en/pdf/otrs_developer_book.pdf but 3.0 is OK: ftp://ftp.otrs.org/pub/otrs/doc/doc-developer/3.0/en/pdf/otrs_developer_book.pdf i'm using Ubunut 8.04, thanks. - Never