2889 errors from Mac users printing lpd

I am getting 2889 errors from Mac users that are connected using LPR to a Windows 2008 R2 print server.

I have it configured to prevent cleartext binds already.

Any ideas?

The following client performed a SASL (Negotiate/Kerberos/NTLM/Digest) LDAP bind without requesting signing (integrity verification), or performed a simple bind over a cleartext (non-SSL/TLS-encrypted) LDAP connection.
 
Client IP address:
x.x.x.x:64148
Identity the client attempted to authenticate as:
"Domain"\"Mac computer"$

"Domain"\"Domain user"