A map description is required for packaging.
Solution
Complete 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 know who made the data, where it came from, and when and how it was made. Descriptions can be added in the Map Properties dialog box's Metadata tab. The Map Properties dialog box can be accessed by right-clicking a map in the Contents pane and clicking Properties.