While Accessing Horde Webmail interface in Plesk it gives following error

Fatal error: Cannot use object of type DB_sqlite as array in D:/inetpub/vhosts/webmail/horde/lib/Horde/DataTree.php on line 656

To fix this error first go to C:/Parallels/Plesk/Additional/Php OR any Directory where Plesk PHP4 is installed and execute Following commands

C:/Parallels/Plesk/Additional/Php>pear upgrade –force pear
downloading PEAR-1.9.0.tgz …
Starting to download PEAR-1.9.0.tgz (291,634 bytes)
…………………………………………………….done: 291,634 bytes
downloading Archive_Tar-1.3.3.tgz …
Starting to download Archive_Tar-1.3.3.tgz (18,119 bytes)
…done: 18,119 bytes
upgrade ok: channel://pear.php.net/Archive_Tar-1.3.3
upgrade ok: channel://pear.php.net/PEAR-1.9.0
PEAR: Optional feature webinstaller available (PEAR’s web-based installer)
PEAR: Optional feature gtkinstaller available (PEAR’s PHP-GTK-based installer)
PEAR: Optional feature gtk2installer available (PEAR’s PHP-GTK2-based installer)
PEAR: To install optional features use “pear install pear/PEAR#featurename”C:\Parallels\Plesk\Additional\Php>pear upgrade –force DB
WARNING: “pear/DB” is deprecated in favor of “pear/MDB2”
downloading DB-1.7.13.tgz …
Starting to download DB-1.7.13.tgz (132,246 bytes)
………………………..done: 132,246 bytes
upgrade ok: channel://pear.php.net/DB-1.7.13C:/Parallels/Plesk/Additional/Php>

After that copy the contents of “PEAR/DB” folder to “horde/pear/Db” (where horde is installed). Restart Plesk and try to access Webmail now.