var nChecked = 0;

function hideMsg() {
              document.getElementById("formMsg").style.display = "none";
              return;
}

function valueChk(oElement) {
     var oDiv = document.getElementById("errMsg");
    if(oElement.checked  === false) {
         nChecked = parseInt(nChecked) - 1;
         oDiv.innerHTML = "";
    } else {
        if(parseInt(nChecked)  >= 2) {
            oDiv.style.color = "red";
            oDiv.innerHTML = "Es können nur bis zu 2 Themen ausgewählt werden";
            document.triggerForm.elements["form[7][" + oElement.value + "]"].checked = false;
            return;
        }
       nChecked = parseInt(nChecked) + 1;
    }
}