You are running a new version of the database server, and you have just opened a database for the first time with this level of the software. The database server has tried to upgrade the database automatically, probably by defining an additional system catalog table. However, it needs to lock the database for exclusive use to do this conversion, and some other user has the database open. Wait a short time, and try this statement again. At that time, the database might be free (or another user's action might have updated it).