Due to the nature of service broker, errors don't occur at the client but rather your messages go in to Service Brokers sys.transmission_queue and are then subsequently processed. If they fail, they stay in the queue. Some errors can be resolved, i.e. missing services. However, others can't, or are just plain difficult. I.e. You've misspelt something, or not used the correct security.
To clear your transmission queue you need to end the conversations, this is a handy little script for doing this. Be aware this ends ALL conversations in the queue and so should NEVER be used on a production system.
To see how many messages are in your transmission queue, use this
SELECT COUNT(1) FROM sys.transmission_queueOn my system i7, DB on Raid10, Log on Raid1, the following clears messages at approximately 20000/second.