If there are many messages in the message control queue, the Service Engine may respond very slowly or not at all. To ensure responsiveness, the number of messages allowed in the queue has been limited.

As of build 100834, this applies to all versions from 8.20:

• Message Control can manage up to 1000 messages in the queue.
  If this number is exceeded, then:
• new messages are rejected and not queued
• an error is displayed in the Diagnosis Viewer