Drop the subscriptions before dropping the publication. If you use SQL Server Management Studio to drop the publication, it will give you the option to automatically drop all associated subscriptions before dropping the publication. If you use stored procedures, you must explicitly drop the subscriptions first. For more information, see Delete a Push Subscription and Delete a Pull Subscription.
If no subscriptions appear to exist for the publication or if you see this error when you create a publication, you might have a previous subscription that was not completely cleaned up when it was removed. Execute sp_removedbreplication (Transact-SQL) on the database to remove all objects and settings related to replication.