[horde] Horde for groupware 4 installation problem

[Pasqualino]

Hello everybody,

I'm trying to install Horde for groupware (version 4) on my shared 
hosting (at Arvixe) following the instructions reported on the official 
guide regarding the operative system independent installation. 
(http://www.horde.org/apps/horde/docs/INSTALL Step 3.1).
At the end of the guide is required to include following commands in the 
.htaccess file:
php_value include_path <path>/horde/pear/php
SetEnv PHP_PEAR_SYSCONF_DIR <path>/horde
On my hosting isn't allowed put php directives in the .htaccess file, 
it's required to put it in a php.ini, so I've created a php.ini file for 
the first instruction (include_path = <path>/horde/pear/php) and a 
.htaccess file for the second (SetEnv PHP_PEAR_SYSCONF_DIR <path>/horde) 
but also in this way if I try to access to the home page I always get a 
page with the following Warnings and Fatal Errors:
Warning: require_once(Horde/Autoloader/Default.php) 
[function.require-once]: failed to open stream: No such file or 
directory in <path>/horde/lib/core.php on line 44

Fatal error: require_once() [function.require]: Failed opening required 
'Horde/Autoloader/Default.php' 
(include_path='<path>/horde/lib:.:/usr/lib/php:/usr/local/lib/php') in 
<path>/horde/lib/core.php on line 44

If I set testdisable=false in conf.php the test.php page is displayed 
without blocking problems (red lines)
I also verified that the Horde/Autoloader/Default.php exist.

What's wrong ?
Do I need some other configuration to activate the site ?

I'm sure that, with your wide experience, you'll be able to help me.
Best Regards.