Unleashed error message "Is-Partial" API when changing Chanalization

[rob_harmsen_5i8]

Hi,

I have 2 R510 AP's with the latest Unleashed firmware (200.13).
When I want to change the chanalization on both 2,4Ghz and 5Ghz from AUTO to 20Mhz and 40Mhz an error message appears:

Is-Partial API Body Invalid

I don't understand what is missing. I cannot find any reference. AP's have been rebooted but no change. Can anyone advice?