HTML checkbox onclick not working in IE11

I have the following code:

  <input name="SLSFrageFeld_Frage050016_Frage05001701" type="checkbox" onblur="this.style.backgroundColor='';" onclick=" return showSB();" onfocus="this.style.backgroundColor='yellow';"/>

However, when I click on the resulting checkbox, the event onclick is not being fired. I am testing it with IE11.