In the agent installation directory, there is an application called 'su' that is used by the agent. If you are getting the <Create process failed for su> error, then the 'su' application is missing.
To fix this, copy the 'su' application from a r11.3 SP4+ agent to the agent that is missing the application. Then restart the agent.
NOTE: You can copy the 'su' application from either a Workload Automation AE Agent or a Workload Automation System Agent.
You can copy the 'su' application from a 32-bit agent to a 64-bit agent or a 64-bit agent to a 32-bit agent.
The source and target agents do not have to be the same exact build.