install new roundcubemail fisrt step error

[adamast]

dear all

i installed rouncubemail at pleask 9
why if open
httP://my-domain/round/installer

error like this

Checking PHP version
Version: OK(PHP 5.2.6-1+lenny9 detected)
Checking PHP extensions

The following modules/extensions are required to run Roundcube:
PCRE: OK
DOM: OK
Session: OK
XML: OK
JSON: OK

The next couple of extensions are optional and recommended to get the best performance:
FileInfo: NOT AVAILABLE(See http://www.php.net/manual/en/book.fileinfo.php)
Libiconv: OK
Multibyte: OK
OpenSSL: OK
Mcrypt: OK
Intl: NOT AVAILABLE(See http://www.php.net/manual/en/book.intl.php)
Checking available databases

Check which of the supported extensions are installed. At least one of them is required.
MySQL: OK
MySQLi: OK
PostgreSQL: NOT AVAILABLE(Not installed)
SQLite (v2): NOT AVAILABLE(Not installed)
Check for required 3rd party libs

This also checks if the include path is set correctly.
PEAR: OK

Warning: include_once(MDB2.php) [function.include-once]: failed to open stream: No such file or directory in /usr/share/psa-horde/roundcube/installer/utils.php on line 40

Warning: include_once() [function.include]: Failed opening 'MDB2.php' for inclusion (include_path='/usr/share/psa-horde:/usr/share/psa-horde/lib:/usr/share/psa-pear:.') in /usr/share/psa-horde/roundcube/installer/utils.php on line 40
MDB2: NOT OK(Failed to load MDB2.php; See http://pear.php.net/package/MDB2)
Net_SMTP: OK
Mail_mime: OK
Checking php.ini/.htaccess settings

The following settings are required to run Roundcube:
file_uploads: OK
session.auto_start: OK
zend.ze1_compatibility_mode: OK
mbstring.func_overload: OK
suhosin.session.encrypt: OK

The following settings are optional and recommended:
date.timezone: NOT OK(Could be set)