A layer description is required for packaging.
Solution
Fill in the layer's description before creating a layer package.
More information
When packaging content, it is important to provide descriptions for your layers so that consumers of a 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 layer properties and populating the appropriate fields. The Layer Properties dialog box can be accessed by right-clicking the layer in the ArcMap table of contents and selecting Properties or by right-clicking the layer file in the Catalog window and selecting Properties.