I deleted a couple of databases from our system, however, they are still being backed up nightly. How can I delete them from our nightly backup plan? I've right clicked on the database and selected deleted but get error messages that prevent the deletion. Any suggestions? Someone advised me to unattach the database. Does that mean to use the detach option and what will that do?

How can you right-click the database if you deleted the database?

Are you using Maintenance Plans for your backups?

Could you provide some screenshots of what you are trying to do? 

Even though the database is deleted from Infinite Visions, it is still appearing in the SQL Server list of databases. I just want to clean up the list of databases on the SQL Server side. 

That is normal for such backup tool that the databases remains for some periode, how else could you restore an accidentally deleted database, if it immediatly disapear from the list?

Apparently screenshots/images are not permitted here.....

So apparently you application (whatever Infinite Visions is) doesn't delete (DROP DATABASE) the database from SQL Server when you remove it from your app. Sloppy app. If you want it gone, you apparently will have to remove it from SQL Server, quite simply!

What error you getting when trying to delete DB's from SQL server ?

Someone advised me to unattach the database. Does that mean to use the detach option and what will that do?

When you delete the database its gone along with database files and when you detach a DB, its removed from the sql serve instance but the DB files reside in the physical path. This option is normally used  when we would require to attach it back after sometime. You could also try this method and once you detached you could delete the physical files as you don't need them a

Apparently screenshots/images are not permitted here.....

You also mentioned that you get error atlest you can paste the error. Are you running script job to backup or you use MP to backup.

Does databases appear in

select * from sys.master_files