This error appears in the $WEBSHPHERE_HOME/WebSphere/AppServer/profiles/<profile_name>/logs/<server_name>/SystemOut.log file.
WSVR0244E: An undefined HOST product variable has been encountered in the krb5Spn property of the $WEBSPHERE_HOME/WebSphere/AppServer/profiles/<profile_name>/config/cells/nullNode01Cell/security.xml#KRB5_1 configuration object.
This error will appear when there is a problem with the krb5Spn option in the security.xml file.
krb5Spn="WAS/${HOST}"
Chaning krb5Spn to the hostname of your WebSphere server should resolve this error.
krb5Spn="MyHostname"