Please make sure NOT to use TableLog components in a high-load test. It is meant to be used for debugging purposes only. We're fixing this issue, but currently this is the most likely reason for the GUI to freeze.
Regarding agents, we usually do not have problems with up to 10 agents running intensive loads. But notice that each agent can simulate several users! Make sure to set the "burst size" on the Fixed Rate Component, for example, as this is what actually represents number of users. And you can have several Generators in each agent, up to the limit of your agent's system.
Let us know if you still need assistance getting highly-intensive load tests running with LoadUI!
Regards,
Renato
SmartBear Software