I have seen this a few times recently. In each case it occurred because of a restored database! Basically, there was an existing published database in the test environment which was correctly configured, worked normally and which showed up correctly in replication monitor. Someone then restored a backup from production on top of this test database without first removing the subscriptions and the publication.

Replication monitor at this stage shows the publication still existing but with an error. In this case running sp_removedbreplication, sp_droppublication, restarting the SQL Server service and the like will not solve the issue – still the replication monitor shows an error. I have tried removing some of the system metadata in the distribution database, which also failed to remove the error. Ultimately the only way I found to remove the publication from the replication monitor was to recreate a publication with exactly the same name and then delete it. 

The dummy publication only needs the same name – the articles can be anything from the database – and once deleted the replication monitor registers the change. No doubt there will be some sort of system proc to do this properly at some stage and I’ll update this entry.