[Dovecot] [Sieve] Sendmail problem

Hi All, it's my first post in this list. I'm running dovecot 1.0.rc15 on my Debian Etch box. It's working very well but I faced a problem with Vacation using Sieve. :-( In fact, after well configuring the system I dont't receive the vacation message, and in the log I found:

deliver(my@address.test): "2008-01-19 12:05:32 "Info: cmusieve: Using sieve path: /home/path/to/my/homedir/.dovecot.sieve deliver(my@address.test): "2008-01-19 12:05:32 "Error: Sendmail process terminated abnormally, exit status 75 deliver(my@address.test): "2008-01-19 12:05:32 "Info: sieve runtim error: Vacation: Error sending mail.

Any idea about the reason this happen and how to solve?

Thank a lot for your help Roger