That means you're either importing it into the wrong category, or it's 1 or 2 pixels off. If, for example, you have a charset sized at 144/287, you have to take it into paint and make the canvas 1 pixel bigger. That doesn't usually happen, though. Just make sure that if you're importing music, you click on the music file first, if you're importing a battler, click on the battle char set file, etc.