Do you know why if fail at loading the plugin ldapdb?

giu 25 18:27:16 ALESSAND-F1E8 syslog-ng[5921]:
ldapdb_canonuser_plug_init() failed in sasl_canonuser_add_plugin():
invalid parameter suppliedgiu 25 18:27:16 ALESSAND-F1E8
syslog-ng[5921]: _sasl_plugin_load failed on sasl_canonuser_init for
plugin: ldapdbgiu 25 18:27:16 ALESSAND-F1E8 syslog-ng[5921]:
DIGEST-MD5 common mech freegiu 25 18:27:16 ALESSAND-F1E8 systemd[1]:
Started System Logger Daemon "default" instance.