Two switches, or a switch and the mode channel, are set to the same job

What ArduPilot says:

• PreArm: Mode channel and RCN_OPTION conflict
• PreArm: Duplicate Aux Switch Options

Each RCn_OPTION gives a channel one function (arm, RTL, a camera trigger). “Duplicate Aux Switch Options” means two channels have the same function, so ArduPilot cannot tell which one to obey. “Mode channel and RCn_OPTION conflict” means the channel that selects the flight mode (FLTMODE_CH) also has an RCn_OPTION.

What to do, most likely first

1. The same number is in two RCn_OPTION parameters.

   CheckList every RCn_OPTION that is not 0 and look for a value that appears twice.

   FixSet one of the two to 0, or to the function you meant.

2. The flight mode channel was given a switch function as well.

   CheckThe message gives the channel: it is FLTMODE_CH, and its RCn_OPTION is not 0.

   FixSet that channel's RCn_OPTION to 0, or move the flight modes to another channel with FLTMODE_CH.

Parameters to look at

Where to do it:Setup & Tuning Guide