Problem
You attempted to start a channel or client application connection. The start failed and found the CSQX631E (z/OS) or AMQ9631 (other platforms) in the error logs.
Cause
The CipherSpecs on each end of a channel do not match.
Resolution
Alter the channel definitions and/or client application so that each end of the channel specifies the same CipherSpec. See here for more information here.
More info here.