Your MIDI keyboard may have a setting that will correct this. Some MIDI keyboards have a clock setting that must be set to EXTERNAL CLOCK ON. This is common in certain Yamaha keyboards that have been reported to be problematic when used with the iTwo. If you are experiencing latency or drop outs then you should see if your keyboard has an external clock setting.
The step by step procedure for enabling the external clock source will vary by manufacturer and model. Please check your keyboard manufacturer's documentation for guidance.