When debugging is enabled for com.sun.security.auth.module.Krb5LoginModule and the file specified by "keyTab" is not found, Krb5LoginModule simply emits a generic message, similar to this:
"Key for the principal foobar@acme.com not available in /home/foobar/foobar.keytab"

This message can be quite confusing and counterintuitive if the file is actually not there, because, based on the message, one would think that the JVM probed the file, found it, loaded the data, but still could not use the keytab data for authentication.