What type of flow control valve do you have?  If you are using a PWM valve, it is not uncommon to get that error if the system uses a large solenoid.  The PWM driver on the GS rate controller is limited to 2.5A output and you can test if this is the issue by lowering the PWM High Limit to 50% and see if the error goes away.  Basically, once you drive the valve to open past the point that draws 2.5A you will get this error.  There is a PWM boost box that can be used to alleviate this issue with PWM valves, if you are getting the issue with a standard valve, the valve is likely defective.