Camera can not be triggered with set frame rate.

The possible trigger frequency depends on the camera model in use. CCD cameras change their operation mode from parallel exposure and frame delivery to sequential exposure and frame delivery. Therefore, they can be triggered with app. half of the frame rate.

Some cameras have the IMX Low Latency Mode. If this mode is enabled, only half of the frame rate is possible as trigger frequency. If higher frequencies are necessary, check whether your camera has this property and whether it is disabled. E.g. the DFK 33UX264 has this mode.