A map document description is required for packaging.
Solution
Fill in the map's description before creating a map package.
More information
When packaging content, it is important to provide descriptions for your map so that consumers of a map package will know who made the data, where it came from, and when and how it was made. Descriptions can be added by accessing the map document properties and populating the appropriate fields. The Map Document Properties dialog box can be accessed by clicking File > Map Document Properties on the main menu.