CentOS 5 Server :: SASL Bind Failures - Invalid Credentials

I am setting up a cluster of servers which use Centos Directory Server for control of logins, etc and kerberos for authentication. The basic setup is working fine, I have been able to manually create accounts using the directory console and these accounts seem to work. Now what I want to do is automate the process of creating new accounts. I am writing a perl script which can be run by one of the server administrators, they supply a small number of arguments and it should create a new user in the directory server, and also create a principal in the kerberos.

I want them to be able to do this using their logged-in kerberos credentials, i.e., without having to enter and re-enter their passwords. My first attempt was to use perl modules Net::LDAP and Authen::SASL. I could not get this working so fell back to using ldap command line tools, but even these I cannot seem to get working! When using mozldap tools, as specified in the admin manual, I get the following:

$ /usr/lib64/mozldap/ldapmodify -h ldaphost.mycompany.com -D uid=eharmic,ou=mydept,dc=mycompany -o mech=GSSAPI -o authid=eharmic < ../ldapmod.txt
Bind Error: Invalid credentials
Bind Error: additional info: SASL(-14): authorization failure:

Using openldap tools I strike exactly the same problem:
$ ldapmodify -Y GSSAPI -H LDAP://ldaphost.mycompany.com -D uid=eharmic,ou=mydept,dc=mycompany -U eharmic < ../ldapmod.txt
SASL/GSSAPI authentication started
ldap_sasl_interactive_bind_s: Invalid credentials (49)
additional info: SASL(-14): authorization failure:

I believe I have set up the mapping correctly:
dn: cn=MyMapping,cn=mapping,cn=sasl,cn=config
objectClass: top
objectClass: nsSaslMapping
cn: MyMapping
nsSaslMapRegexString: ^(.+)@MYCOMPANY.COM
nsSaslMapBaseDNTemplate: ou=mydept,dc=mycompany
nsSaslMapFilterTemplate: (uid=1)

It must be getting reasonably far because after doing the above I can see the LDAP service ticket in my "klist" output.