I've been running in to this issue a lot lately while in the process of upgrading our servers from 5.2 to 5.3 SP1. When I try to do an offline migration export, once I select the source system I get an error in the attached screen shot. We are using SQL server to host the Adeptia Log database, and I'm fairly certain that connectivity is fine, because I can look at the details of all the process flow logs via the browser interface.
1) Download the SQL Driver files that are available for download here: http://www.microsoft.com/en-us/download/details.aspx?displaylang=en&id=11774.
2) Copy the sqljdbc4.jar file into the \AdeptiaServer\ServerKernel\MigrationUtility
3) Rename the sqljdbc4.jar to sqljdbc.jar
4) Run the Migration Utility again