Browser is telling me there is no file called "arrows_1.png". You probably have an incorrect file path to the image.
.nivo-directionNav a {
position:absolute;
top:45%;
z-index:1000;
cursor:pointer;
display:block;
height: 30px;
width: 30px;
text-indent:9999px;
background: url(arrows_1.png);//here is the error.
background-repeat:no-repeat;
opacity: 1; /* NEW */
-webkit-transition: all 200ms ease-in-out;
-moz-transition: all 200ms ease-in-out;
-o-transition: all 200ms ease-in-out;
transition: all 200ms ease-in-out;
}