Cannot drop the database because it is being used for replication.
In the event you want to move a database that is configured as a publisher for replication, a detach/attach will not work. Rather, you can simply take the database offline, move the data file, adjust the properties and bring it back online. I saw suggestions to backup/restore, but this is much quicker and more effective in my opinion.
ALTER DATABASE <database name> SET OFFLINE
-- move file to new location
ALTER DATABASE <database name> MODIFY FILE ( NAME = <logical file name>, FILENAME = '<path\file name>')