The search and create case capabilities of Dovetail Mobile Agent depend on the search product Dovetail Seeker. The create case feature requires that the Dovetail Seeker configuration is updated to add a document specification for contact search. This is included with Dovetail Seeker 2.0
Make sure Contacts are configured as a valid search domain within Dovetail Seeker. This is accomplished by having a Dovetail document specification present within the documentSpecifications.xml file with the displayName of Contact. An example is provider in the documentSpecifications.xml file that ships with with Dovetail Seeker.
Follow the Dovetail Seeker instructions for re-indexing your search index.