After much searching and hair pulling out as 50K email accounts on my server quit working it seems that the Perl RPM in CentOS *Plus* is broken (missing XS that Zimbra needs during install) but the Perl that comes with CentOS (non-Plus) has XS in it. See the below link on how to restore back to the plain Perl with XS support. After I did this my upgrade went perfectly. Everything else in the above posts did not work for me.
[SOLVED] CentOS is NOT supported