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Continua CI uses WCF between the agent and the server, if the clocks of the agent and server machines are too far apart (more than 5 minutes), the agent will gets an exception while registering :
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"An unsecured error or incorrectly secured fault was received from the other party. See the inner fault exception for the fault code and detail.
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System.ServiceModel.FaultException: An error occurred when verifying security for the message"
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