Challenge pages cannot be totally disabled. From CF's admin page:
Adjust your basic security level to modify CloudFlare's protection behavior. A low security setting will challenge only the most threatening visitors. A high security setting will challenge all visitors that have exhibited threatening behavior within the last 14 days. Essentially off will act only against the most grievous offenders. We recommend starting out at medium.
Adjust your basic security level to modify CloudFlare's protection behavior. A low security setting will challenge only the most threatening visitors. A high security setting will challenge all visitors that have exhibited threatening behavior within the last 14 days. Essentially off will act only against the most grievous offenders. We recommend starting out at medium.