[imp] raiseError with IMP browsing INBOX

[Riccardo Riva]

Hi all,

I have a problem using IMP (I've tried a lot of version) when i browse 
the INBOX.
IMP tell me :
Fatal error: call to undefined function raisererror() in 
/usr/share/php/Mail/RFC822.php

If I delete some message IMP restarting work correctly but I can't see 
anything wrong in the message deleted.

Horde or Apache log files don't tell anything.

What can you think can be, and more important in which way could I solve 
it ?

Thank you
Riccardo