change error message according to discussion
change error message according to discussion

ktakashi/picrin,ktakashi/picrin,koba-e964/picrin,leavesbnw/picrin,dcurrie/picrin,koba-e964/picrin,koba-e964/picrin,leavesbnw/picrin,picrin-scheme/picrin,omasanori/picrin,dcurrie/picrin,picrin-scheme/picrin,ktakashi/picrin,leavesbnw/picrin,omasanori/picrin