Cant run Roundcube, (Failed opening 'PEAR.php' for inclusion)

[gonace]

[22-Jul-2010 18:28:08] PHP Warning:  Adding option (Name: suhosin.session.encrypt Value: 0) (23, 1) failed!
 in Unknown on line 0

[22-Jul-2010 18:28:08] PHP Warning:  include(W:\System\webmail\PEAR.php) [function.include]: failed to open stream: No such file or directory in W:\System\webmail\program\include\iniset.php on line 106

[22-Jul-2010 18:28:08] PHP Warning:  include() [function.include]: Failed opening 'PEAR.php' for inclusion (include_path='W:\System\webmail/;W:\System\webmail/program;W:\System\webmail/program/lib;W:\System\webmail/program/include;.;C:\php5\pear') in W:\System\webmail\program\include\iniset.php on line 106

[22-Jul-2010 18:28:08] PHP Fatal error:  Class 'PEAR' not found in W:\System\webmail\program\include\iniset.php on line 129


Don't understand why