Following the removal of the egroupware packages from testing and
unstable because they were unmaintained and have outstanding unaddressed
security issues for a while the packages got now removed from
lenny-backports, too.
If you have installed the egroupware suite please be aware that they
aren't maintained since a long while now and do contain some more
severse security issues. Unfortunately I'm not aware of a replacement to
suggest, so you either will have to track the groupware suite yourself
or look for an alternative.
Sorry for the inconvenience,
Rhonda