The error is typically a result of an inconsistent configuration.
Usually a value for AutoServerPort or UseEncryption, the $AUTOUSER/config.$AUTOSERV file(s) do not match between the two AE hosts and/or WCC.
Additionally confirm consistent values are being used for the EnablePmux and EnableSSL settings in csampmux.
Run the following to review the csampmux settings (run this on all AE and WCC hosts as root) :
$CSAM_SOCKADAPTER/bin/csamconfigedit port=<AutoServerPort> display
$CSAM_SOCKADAPTER/bin/csamconfigedit portrange=49152-50176 display
Example of how to change a value:
$CSAM_SOCKADAPTER/bin/csamconfigedit port=9000 EnablePMUX=True
NOTE: A restart of the application server would be needed to reflect any changes if they were made on the Workload Automation AE application server(s).