Question: how to fix an error has occurred on 3ds?
Answer: STEP 1: Open your Nintendo 3ds and locate the wi-fi card.
STEP 2: Unplug the wi-fi card. Be careful while doing this. ... 
see picture below of the wi-fi unplugged.
STEP 3: Now pop it back in until you hear a click. Some times, it takes two clicks to ensure that it has been firmly seated back.