[imp] Horde + MySQL problems : Fatal error: Call to a member function on a non-object in /var/www/html/horde-2.1/lib/Registry.php on line590

[Tony Click]

I'm getting the above error message when I try to access horde preferences
in MySQL.  I've installed twice before and both installs are still working,
so I'm reasonably confident that the steps I'm following are pretty close.

So either I've accidently misconfigured something, which I cannot find - In
that case I'm hoping a fresh set of eyes can tell me what I've done wrong -
or -
on this particular configuration I'm using something that isn't compatible
(which is entirly possible since the previous installs were on two different
versions of RedHat)

Things of note:
RedHat 8.0
Apache 2.0.40
MySQL 3.23.53
Pear 1.0.1
Horde 2.1
Imp 3.1
Turba 1.1
Passwd 2.1
PHP 4.2.2

Everything is good on the horde/test.php screen except MCAL and Mcrypt

If I set (horde.php) $conf['prefs']['driver'] = to either 'session' or ''
IMP works, but of course turba does not.

Any thoughts?