Dovecot con Autentication Checkpassword error signal 111

[zerocool at modemsoft.it]

Good morning,
It is the first time I write in this mailing list and I apologize in  
advance for possible nonsense that i can write.
I have a mail server with qmail + courier imap and I would "Migrate"  
to dovecot.
I installed the package and configured the components necessary to me  
using as system autentication checkpassword.
I have verified the checkpassword operation without the processor  
usage of Dovecot and is functioning.
When you perform the tests with dovecot from the logs out these errors:


auth: Error: checkpassword(plutos,127.0.0.1,<WLcLPkg8esF/AAAB>): Child  
15375 died with signal 11
auth: Error: checkpassword(plutos,127.0.0.1,<WLcLPkg8esF/AAAB>): Child  
15376 died with signal 11
imap-login: Info: Disconnected (auth failed, 2 attempts in 8 secs):  
user=<plutos>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, secured
master: Warning: Killed with signal 15 (by pid=15479 uid=0 code=kill)

or :

auth: Error: checkpassword(plutos,192.168.1.113,<zzV561I8IuDAqAFx>):  
Child 15851 died with signal 11
auth: Error: checkpassword(plutos,192.168.1.113,<zzV561I8IuDAqAFx>):  
Child 15852 died with signal 11
imap-login: Info: Disconnected (auth failed, 2 attempts in 8 secs):  
user=<plutos>, method=PLAIN, rip=192.168.1.113, lip=192.168.1.113,  
secured
imap-login: Info: Disconnected: Too many invalid commands (no auth  
attempts in 102 secs): user=<>, rip=192.168.1.235, lip=192.168.1.113
auth: Error: checkpassword(plutos,192.168.1.235,<7pLd+FI81uXAqAHr>):  
Child 15870 died with signal 11


It is already a long time that we slam but I can not figure out where  
to make the mistake. Who will help me to solve this problem.

Thanks in advance for your support.

Regards