switching sums

it kept saying and error has occurred when i was trying to change my shaco sums flash to smite... it wouldnt let me and i tried it 3x.. kept getting same message let me change my runes during selct.. but after in que it showed as my teemo page so it never change ether during.. but the error only popped up when i was doing my sums.. had time to do it just wouldnt let me...