I have found the solution in order to fix this. The problem is that the lib90-... is not compatible with Version 1.2.17, so in order to solve this I installed dovecot again from rpms like this :
PLEASE BACK UP ALL YOUR DATA LIKE dovecot.conf and dovecot-sql.conf (you might want to search and backup also dovecot.conf.rpmsave) from /etc/
first is to stop dovecot: /etc/ini.d/dovecot stop
remove dovecot without dependencies: rpm -e --nodeps dovecot
download it : wget http://centos.alt.ru/pub/dovecot/1.2...el5.x86_64.rpm
install from rpms : rpm -i dovecot-1.2.16-1.el5.x86_64.rpm
then edit /etc/dovecot.conf and paste the content from the old dovecot.conf.rpmsave or dovecot.conf depending what is your previous working backup version.