MacBook Pro - Excel - Workbook Password Protection problem...

I'm trying to password protect an Excel file (Microsoft Excel for Mac 2011, v14.3.8), but I'm receiving a message that reads:

"Your computer isn't set up to use restricted permissions. Open a rights protected document or email message from someone within your organization to set it up."

Here's how I'm trying to password protect the file:

File > Restrict Permissions > Restricted Access (or "Manage Credentials")

This is my personal laptop. I'm the only user (besides a Guest account) on the computer. I have admin permissions on my user profile. What do I need to do in order to change this so I can password protect Excel files?