internet explorer does not display correct font is custom css and firefox and chrome do correctly

heres my custom css for main navigation.Which internet explorer can not display with the specified font.It works fine in firefox and chrome,please tell me how to correct this issue with IE9

Thanks in advance.

.MSC_PrimaryNavLink
{
color:#FFFFFF !important;
font-size:18px;
font-weight:bold;
font-family: "sans-serif";
text-decoration:important;
}
.MSC_PrimaryNavLink:hover
{
color:#FF0000 !important;
font-size:18px;
font-weight:bold;
font-family: "sans-serif";
text-decoration: !important;
}
.MSC_PrimaryNavFrame a{font-size:18px !important;

}
a:link {
COLOR: Red;
font-family: "sans-serif";
}