gdbm fatal: read error (man pages)

I've been getting gdbm fatal: read error when trying to use man pages recently. Does anyone know what this might mean? A fix is to remove /usr/local/man from the MANPATH. There is actually nothing in /usr/local/man except the standard man* folder. All the permissions in /usr/local/man are the same as those in /usr/share/man. All suggestions welcome. JDL