[horde] Problem with pear

[Nusa]

I'm re-installed my server and I'm the same problem : 

Fatal error: Call to undefined function: is_a() in /usr/share/pear/PEAR.php
on line 244

If, I donwgrade pear (pear-1.2), I've an other problem :

Warning: Failed opening 'Log.php' for inclusion
(include_path='.:/usr/share/pear') in /var/www/horde/lib/Horde.php on line
186

Who installed with success horde on a debian 3.0 rc2?

Thank you for your help

Charles