When the Obtain Kerberos v4 credentials button is checked, NetIdMgr will attempt to retrieve Kerberos v4 credentials when ticket initialization, renewal, or importation is performed. Kerberos realms are increasingly configured to support only Kerberos v5 (e.g., Windows Active Directory Domains.) If the realms you use do not support Kerberos v4 it is suggested that this button be unchecked.
Be aware that only the default identity can obtain Kerberos v4 credentials. This limitation is due to the inability of Kerberos v4 applications on Microsoft Windows to specify a credentials cache.