Error message "does not have an API" and no login

Hi, 
after a server reboot (Linux CentOS 6.5, apache 2.2.5) our users can't login to horde webmail anymore. 

With correct credentials (tested in /test.php/?app=imp and are OK) the user can't login and the messages we obtain are: 

[...] 
HORDE: [horde] trean does not have an API [pid 14500 on line 891 of "/usr/share/pear/Horde/Registry.php"] 
HORDE: [ingo] trean does not have an API [pid 17120 on line 891 of "/usr/share/pear/Horde/Registry.php"] 
[...] 

All the check in /test.php seems OK: 

- Horde 5.1.6 
- PHP Version: 5.3.3 
[...] 
- PEAR Search Path (PHP's include_path): /var/www/horde/lib:/var/www/horde/lib:.:/usr/share/php:/usr/share/pear 
- PEAR: Yes 
- File_Fstab: Yes 
- Net_DNS2: Yes 
- Services_Weather: Yes 

Some PHP modules are not loaded: 
- LZ4 Compression Support (PECL extension) 
- MongoDB support (PECL extension) 
- PAM Support (PECL extension) 
- PostgreSQL Support: 

Sorry, I'm not expert in horde framework. 
How can I dig more in deep this problem? 

Thanks for any help, 
Carlo 

-- 
Carlo Todeschini 
Project Manager 

Metarete Srl 
Via Mantova, 71 - 26100 Cremona - Italy 
C.F/P.I. e N. Iscr. Reg. Imprese di Cremona: 01219750195 
Capitale Sociale: 32.000€ i.v. - PEC [email protected] 
Tel: +39 0372 432228 - Fax: +39 0372 590617 
http://www.metarete.it - [email protected] 
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