Error in Horde(Webmail)

While trying to browse webmail using webmail.domainname.com it shows following error:
Warning: main(PEAR.php) [function.main]: failed to open stream: No such file or directory in D:\I
netpub\vhosts\webmail\horde\lib\core.php on line 26

Warning: main() [function.include]: Failed opening 'PEAR.php' for inclusion (include_path='D:\Ine
tpub\vhosts\webmail\horde\lib

;.;./includes;./pear') in D:\Inetpub\vhosts\webmail\horde\lib\core.php on line 26

Open core.php file of horde: C:\Inetpub\vhosts\webmail\horde\lib\webmail\horde\lib\core.php

change this:
ini_set('include_path', dirname(__FILE__) . PATH_SEPARATOR . ini_get('include_path'));

To:
ini_set('include_path', 'C:/Inetpub/vhosts/webmail/horde/lib' . PATH_SEPARATOR . 'C:/Inetpub/vhosts/webmail' . PATH_SEPARATOR . 'C:/Inetpub/vhosts/webmail/horde/pear' .PATH_SEPARATOR . ini_get('include_path'));