I had this problem, too, but I also found a work-around...
You have to fill in the fields CONEX_LDAP_CHECK_FIELD2_NAME, CONEX_LDAP_CHECK_FIELD2_VALUE and CONEX_LDAP_CHECK_FIELD2_ROLE with the same values of CONEX_LDAP_CHECK_FIELD1_NAME, CONEX_LDAP_CHECK_FIELD1_VALUE and CONEX_LDAP_CHECK_FIELD1_ROLE respectively.
This way you can connect with your LDAP user, at least (provided that the remaining infos are correct, of course).
As soon as my GitHub account is activated, I'm going to file this bug (https://github.com/OCSInventory-NG/OCSInventory-Server/issues
)... hoping it will get fixed soon
UPDATE - bug opened: https://github.com/OCSInventory-NG/OCSInventory-Server/issues/80