Having configured my Service Bus, I realised that I should have used a different service account. Doh! Time to roll back the configuration and start from scratch. So this is how it went:
1) Remove the namespace created for the Service Bus Host; Used Remove-SbNamespace -Name and the namespace is gone.
2) Next, remove my machine from the Service Bus farm; Used Remove-SbHost and my server is de-registered from the SB Farm. Easy Peasy Lemon Squeezy!
3) Next was to remove the Service Bus farm; so thought will run Remove-SbFarm. Hang on a minute! There is no such thing as Remove-SbFarm. So I tried to re-configure my farm but my PowerShell console kept shouting “The database (SbManagementDB) located at SQL Server (.) is already configured.”
Right! Let me try the conventional UnInstall–> ReStart–>ReInstall–>ReStart routine on the Service Bus to get rid of this problem. But as soon as I got to configuring the service bus the same message popped up again. So in-spite of doing a complete ReInstall the Service Bus still says its configured. Spooky! Well, not really. A bit of probing and I realised that the problem is with these databases:
These databases are not deleted even if the product is UnInstalled. I manually deleted these databases and tried configuring the Service Bus again, voila, this time it worked like a charm. So let me re-word Step (3) as:
3) Next was to remove the Service Bus farm; login to your SQL box and manually delete SbGatewayDatabase, SbManagementDB and ServiceBusDefaultContainer. Fire away!
VeeN
btsbee.wordpress.com 
Hi
I am faced with a similar issue and want to start from scratch. In my case I simply used the New-SBFarm commandlet. and so explicit namespace.
Yikes I meant no explicit namespace