Here is the daily misadventure :
Having a ZCS Network Edition 5.0.10 for Ubuntu6 under Debian Etch, I decided to upgrade to the new stable release Lenny (Debian stable 5.0).
Debian users/administrators know this well... When rebooting (because of new kernel version) Zimbra's services were not starting.
After reboot trying by hand :
$ su zimbra
$ zmcontrol start
/usr/bin/perl: symbol lookup error: /opt/zimbra/zimbramon/lib/i486-linux-gnu-thread-multi/auto/IO/IO.so: undefined symbol: Perl_Tstack_sp_ptr
Ouch... Zimbra seems not to like perl upgrade from 5.8.8 to 5.10.0...
dpkg -i perl_5.8.8-7etch6_i386.deb perl-base_5.8.8-7etch6_i386.deb perl-modules_5.8.8-7etch6_i386.deb
Don't care about these messages
dpkg - warning: downgrading...
It's exactly what we want !
Hope this may be useful to other people. Better simply not upgrade the Perl packages