[imp] Problems with Horde

[Jorge Izquierdo]

I don´t know if this is the right place where asking next question but I´ll
trie. Whe I run the signup.php3 provided with Horde, the browser reports me
next error:

Fatal error: Call to undefined function: page_open() in
/usr/local/apache/htdocs/horde/signup.php3 on line 88


And when I run the test.php3 of Horde it provides me the next information:

PHPLIB Configuration
track_vars: Yes
PHPLIB (is page_open() defined): No

What can I do to get the page_open() defined?

Thanks for your attention, I think this is quite simple so you´ll be able to
lost a few seconds answering me.

Jorge