That error could come because of the amount of messages you are trying to send to the queue, or do to other reasons because the messages are being sent asynchronously. If you do not need the messages to be sent asynchronously then you could try to set property PUTASYNCALLOWED to NO in HermesJMS. That will determine if messages are to be put asynchronously. This is pretty much out of scope for SoapUI Pro and related to WebSphere MQ at this point. Please see
http://publib.boulder.ibm.com/infocente ... 41220_.htm for more information, and look at the IBM WebSphere MQ documentation.
Regards,
Marcus
SmartBear Support