Error -200684 Duty Cycle not valid on any value

I'm using the LabWindows CVI DAQmx Library to write a counter frequency using DAQmxWriteCtrFreq
If it matters, im using LabWindows 2013 ds2 and DAQmx 9.7.5
Im using a PCI-6602 simulated in MAX.
I have a task containing 4 Channels named Freq_Out.
I have an array of frequency values named Freq_Data containing {0.1,1,0.1,5120}
I am using a duty cycle of 0.5.
This returns an error code -200684, which states that the duty cycle is invalid. However i have tried this with many different values across the range 0  - 0.99 and this appears no matter the value.

Any help or advice would be apreciated.