"Add Users" to a protected word document

I have made a vacation request form that employees will fill out on the
computer & submit by email to the owner. The top part of the form is to be
filled in by the employees so in the password protection part I highlighted
the top part and click "everyone" under "Exceptions". The bottom part is
where the owner chooses to accept or deny the request. I highlighted this
whole part and clicked on "more users" to add him as a user. I can't add
him...a box comes up stating "Some of the users you have entered could not be
added to the list because their names could not be verified". I also went
onto his computer, went to control panel, system, and looked up his "computer
name" and "full computer name" and then user profile name (which I think is
domain\name?!?). None of those worked. How do I add him in???

Thank you!