When You're trying to change config and save (example: change DNS) on Fortigate 200B then appears error "CFG_CMDBAPI_ERR", based on to the reference from googling: we can try to turn off some features in UTM such as: IPS.
But it's not always work because many Users told that although they have turned off features in UTM (IPS), error "CFG_CMDBAPI_ERR" still appears.
Error "CFG_CMDBAPI_ERR" appears because of high memory on Fortigate 200B and based on to the my experience, this is true (when Memory Usage of Fortigate 200B reached approximately 85%).
And the solution for this error is ... just rebooting the device and then it works well, we can change DNS. Because after reboot the Fortigate 200B, memory usage only 15%