Are you able to find the queue instance referenced when you view the System-Queue-ServiceLevel instances? If you do see an entry, what is the status? Are there any error messages contained in the XML for the item?
Since you see the queue item is present, I am not sure what is causing the error. I would need to see the Tracer data to see what rules are being executed and understand more about the flow. You may need to open a Support Request so someone can work with you on it.