dovecot - Dec 2012 - pop3-login: Error: SSL: Stacked error:

Hello again

I have few messages in dovecot.log like the following :

Dec 03 15:52:07 pop3-login: Error: SSL: Stacked error: 
error:140943F2:SSL routines:SSL3_READ_BYTES:sslv3 alert unexpected 
message: SSL alert number 10

Anyone could tell what does this means ?

Thank you