slurpd problem!!!

["ganling" <carlingling@163.com>]

hello!
  In my master ldap server, I start the slapd and slurpd processes.But when I modify one entry in it ,the slurpd can't propagate the change to my slave ldap server. I use -d 4 parameter to start slurpd ,and I get error like this:
   error:ldap_modify_s faild modify"constraint violation":cn=ganling,ou=server,dc=fsca,dc=com"

 In the master ldap's slapd.conf ,I write:
     replica host=192.168.0.238:389
             binddn="cn=slave1,dc=fsca,dc=com"
             bindmethod=simple credentials=slave1

In the slave ldap's slapd.conf,I write:
    updatedn="cn=slave1,dc=fsca,dc=com"
    updateref="ldap://192.168.0.246:389";
my master ldap's ip:192.168.0.246
my slave ldap's ip:192.168.0.238,and cn=slave1,dc=fsca,dc=com is rootdn in slave's slapd.conf file.

if i use :./ldapmodify -f mod.ldif -D"cn=slave1,dc=fsca,dc=com" -x -wslave1 
in slave server,it works ,and can modify entry. 
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