namazu: Unterminated compressed integer at [...]

I replaced the harddisc in my FreeBSD (4.5-STABLE) box that runs namazu
and moved all contents 1:1 (using dump and restore) to the new disc. It
seems that now namazu doesn't want to write the index files any longer.

After executing
/usr/local/bin/mknmz -Z --checkpoint -O /mnt/hd2/namazu/questions
--mhonarc /usr/local/www/freebsd/search-de/questions

namazu reads all new mails, then when about to write the index files, it
reports:

Writing index files...Unterminated compressed integer at
/usr/local/bin/mknmz line 2288.

namazu produces threads.html in the output directory just fine, but the
searchable index isn't updated.

Any ideas?

Thanks
Markus