[horde] Problem with pear

[Nusa]

Hi,
I've a home server with Debian 3.0 r2 with qmail. It's OK. I want to install
horde but I've a problem with pear. I'm install pear 1.3 and horde 2.2.5.
When I want to use horde after the identification I've this error message :

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

I see this error in the FAQ, I downgrade pear, no result. I use the last
horde.... I can't modify the php file beacause I don't know the
programmation....

Can you help me please.

Charles