What was found
EMERGENCY EXIT ECAM FOR LEFT OVERWING EXIT DURING CRUISE, THE COVER IS IN AND WAS NOT TOUCHED BY A PASSENGER, NO ABNORMAL VERTICAL SPEED. ECAM CLEARED WITH NO ACTION SOMETIME BELOW 10,000. MAINTENANCE FOUND DUST & DEBRIS ON ACCESS COVER OF THE PROXIMITY TARGET, CLEANED THE TARGET IAW AMM 52-20-00. ACCOMPLISHED SATISFACTORY OPERATIONAL CHECK. AIRCRAFT WAS GROUNDED.