On the GT-400, if a user was enrolled, we were able to send a blank template and that would "un-enroll" the user. That appears to not be working now, why is that?

The reader will not let you overwrite a template if it already has one.  This includes overwriting a template with a zero length (blank) template which would indicate that the user is not enrolled.  The correct way to unenroll a user is to first remove the user and re-add the user in order to obtain the result that you desire.

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