SquirrelMail - Error opening ../data/default_pref

Hi all,
I have my webmail working done untill I change the Apache user.

Afther change the Apache user the webmail stop working. If I try to login ...

ERROR
Error opening ../data/default_pref
Default preference file not found or not readable!
Please contact your system administrator and report this error.
Go to the login page

I can't find this file, I suppose, the problem, is a file permission, but I can't find the place to fix this.

I try to change "/usr/share/squirrelmail/data permission but ... the error still on.

Kind regards
Piero