The US Radar Invalid message on the MFD occurs when the MFD system time is off. 

Power on the avionics

Acknowledge the messages on the MFD

Scroll to the Aux Tab

Select System Time

- If your date and time are off, correct the time (manual) or take the aircraft outside away from all structures, and allow the GPS radios to acquire the signals (GPS or Auto)

- Remember the time changes in the US (Daylight Savings and Standard) impact the unit when set to Manual.

If your GPS radios are feeding the MFD an incorrect date/time, please contact the manufacturer of that device.