[horde] Fatal error: setoption()

[Support]

Hi all,

after installin horde3 on Debian 3.1 i log in to imp and try to open a 
mail. There is the following error:
*
Fatal error*: Call to undefined function: setoption() in 
*/usr/share/php/Horde/History.php* on line *61

**This is History.php line 61:
$this->_db->setOption('portability', DB_PORTABILITY_LOWERCASE | 
DB_PORTABILITY_ERRORS);

Sorry, but is this a php or pear problem?
Has somebody horde/imp running successfully on Debian 3.1?
***