Hi Grant Jex,
Generally this error is thrown when you try to find the DN of a user inside of a specific domain when the user is from another domain.
1. Make sure that the LDAP connection string is correct.
2. Make sure that the connectionString, domainName and Password you use are correct.
3. Make sure that you are able to access the windows contacts using your LDAP://IP
4. If you use dc check whether the spelling of your ds= com, ds = abc
You can gather more information about AD searches from here
All the best,
the Telerik team