I have just found this error on a Zimbra 5.0.6 Open Source Edition running on Debian Etch 32 bits:
2008-06-19 18:29:03 deferred (host 127.0.0.1[127.0.0.1] said: 451 4.5.0 Error in processing, id=29874-14, parts_decode_ext FAILED: file(1) utility (/usr/bin/file) error: run_command (open pipe): Can't fork at /opt/zimbra/zimbramon/lib/i486-linux-gnu-thread-multi/IO/File.pm line 188.
It appears several times in the mail that the admin account receives every day.
The file command is there, and I am quite sure that all the necessary libraries were installed. Here you are the list of extra packages that I installed on a standard system before I installed Zimbra:
curl sudo libidn11 fetchmail libgmp3c2 libxml2 libstdc++5 libstdc++6 openssl libltd13 libssl0.9.7 libdb3 libexpat1 file libltdl3 libio-socket-ssl-perl libmail-imapclient-perl libmail-pop3client-perl libpcre3 file psmisc
Thanks in advance.