[imp] constant already defined

[linux@afcomputer.com]

Hi, i try to install the horde 1.3.4 and imp 2.3.6 but when i go to
http://www.myhost/horde/imp it says this
Warning: Constant no_action already defined in
/var/www/html/horde/imp/lib/IMP.php on line 10

Warning: Constant update_prefs already defined in
/var/www/html/horde/imp/lib/IMP.php on line 28

Fatal error: Undefined class name 'lang' in
/var/www/html/horde/imp/lib/base.php on line 38

horde works well but imp not.
Anyone know why?