Your .PM! address book index file is corrupted. Unfortunately we don't have any modern internal tools to repair address books. There is the old dos-based PMIMPORT.EXE utility that you can extract from the PMAIL/DOS version (v3.5 is available from the download web site). PMIMPORT can extract the data from the address book, you can then check it and clean up any duplicates, then reimport it into a new address book. Note that you can use the Tab key in PMIMPORT to bring up a file/directory selector window when in a field that asks for a filename.