This error has occurred during the first communication for the provisioning process to retrieve the PFX.
This may be caused by exceeding the configured value for Maximum Session Count – this option determines the number of concurrent mobile issuance and update sessions are allowed by the server. See the Mobile Identity Management document for details.
If this error consistently occurs when attempting to provision with Identity Agent, there is most likely a network misconfiguration; for example, with the firewall. In this case, the problem is with accessing the ProcessDriver.asmx service.