To create a mobile account for your Mac OS account to bypass this issue:

1. In the Apple menu, go to System Preferences... .
2. Under the System section, select User Groups .
3. Click the lock icon in the lower left corner.
4. Click Create... next to Mobile account.
5. On the following screens, select any personal settings, and click Create to proceed from one screen to the next.
6. When prompted, enter your Active Directory password and click OK.

Click image to enlarge.

Your mobile account has been created. You may now use this mobile account to initiate encryption.