I didn't see one in the Navigation class. I think putting "border: 0" would fix that.
#navagation li a {
color: #fff;
float:left;
border-right: 1px solid #999;
width:85px;
height:40px;
text-decoration: none;
text-align: center;
line-height: 40px;
font-size: 1.0em;
font-weight: normal;
font-style: normal;
background-position: center;