First, make sure you are using an iPad with 3G. Wifi only iPads are not compatible with MotionX-GPS HD. The do not have the necessary GPS chipset to acquire an accurate signal.
Ensure your iPad has a clear view of the sky. GPS requires a direct ‘line-of-site’ to communicate with satellites. Your iPad must have a clear view of the sky to locate at least three satellites in order to give accurate position information. If you are located indoors, or in a wooded area or urban canyon (surrounded by buildings), you may be unable to acquire an accurate signal.
If you can’t acquire a signal within two minutes, try using “Reset Location Warnings” under the iPad’s settings in General >> Reset.
If you are flying or traveling at speeds above 150 mph/240 km/h, you may wish to switch the Accuracy Filter off under Settings > Global Settings if you are having trouble maintaining a GPS signal. Turning the Accuracy Filter off makes it easier to acquire and maintain a GPS signal when traveling at high speeds.
Alternately, try powering your iPad off, then turn it back on and launch MotionX-GPS. If prompted, allow MotionX-GPS to use Location Services by selecting “Ok”.