The Zimbra install process tells you about missing packages, but it doesn't tell you about all of them. After you install Zimbra, best thing is to login as "zimbra" (or do "su zimbra") and then do
zmcontrol stop
zmcontrol start
When Zimbra restarts you should see error messages if there are any packages still missing. In my case, I found that I still had to install a curl compatibility package, and created a symbolic link so that "libexpat.so.0" resolved to my "libexpat" library.