I am unable to upgrade any 6.0.16 to 7.*, even clean/fresh installs of 6.0.16. Every attempt hangs the first time the 7.* mysql is started with this in mysql-error.log

Code:
121028 21:38:23 mysqld_safe Starting mysqld daemon with databases from /opt/zimbra/db/data
121028 21:38:24 [Warning] '--log_slow_queries' is deprecated and will be removed in a future release. Please use ''--slow_query_log'/'--slow_query_log_file'' instead.
121028 21:38:24 [Warning] '--log-long-format' is deprecated and will be removed in a future release. Please use '--log-short-format' instead.
/opt/zimbra/mysql/libexec/mysqld: Table 'mysql.plugin' doesn't exist
121028 21:38:24 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
121028 21:38:24 [ERROR] /opt/zimbra/mysql/libexec/mysqld: unknown variable 'innodb_buffer_pool_size=633855590'
121028 21:38:24 [ERROR] Aborting

121028 21:38:24 [Note] /opt/zimbra/mysql/libexec/mysqld: Shutdown complete
This happens even when I create a new VMware or VirtualBox VM, install Ubuntu 8, Ubuntu 10 or Debian 5 (all 64-bit) from distribution ISOs make no changes beyond installing the recommended llibgmp3c2, sqlite3 & sysstat, and the zcs tarballs from the zimbra, everything installed with defaults. The 6.0.16 install always succeeds, and the upgrad to 7.* always fails as shown above.

It's clear that conf/my.cnf was not (properly) upgraded. The forums have few complaints of this nature so I'm baffled why such simple & ordinary experiments of mine always fail.

Has anyone seen & gotten around these errors?