What was found
FLIGHT 3018 CHS-LGA - THE FLIGHT TOOK OFF FROM RUNWAY 21 AT CHS, AFTER NOSE GEAR RETRACTION, A LG/AIR GND FAIL MESSAGE APPEARED THE EICAS AND THE LANDING GEAR WOULD NOT RETRACT. THE QRH WAS FOLLOWED AND AN EMERGENCY WAS DECLARED. THE AIRCRAFT RETURNED TO THE FIELD. THE LANDING WAS UNEVENTFUL AND THE MESSAGE CLEARED ITSELF UPON LANDING. MAINTENANCE CLEANED THE PROXIMITY SWITCHES AND RESECURED THE CANNON PLUGS. THE GEAR WAS SWUNG AN NO MESSAGES WERE PRESENT. OPS CHECK GOOD IAW EMB 145 AMM 32-60.