Sorry sorry sorry - hab des Pudels kern...

das "return false" gehört in das OnClick Event und nicht in die Funktion...

Also

<a onclick='TogglePWD(this, 'VUE1');return false;'><input type='image' src='Resources/view.png' name='Button99' value='VUE' id='VUE1' style='width:30px;' /></a>

<span id='XXX1' style='display: none'>**********</span>
<span id='PWD1';'HIER STEHT DAS KLARTEXTPW</span>

function TogglePWD(anchor, IDS) {
            //var CState = document.getElementById(IDS);
            var subclass1 = "PWD" + IDS.substring(3);
            var subclass2 = "XXX" + IDS.substring(3);
            var CState1 = document.getElementById(subclass1);
            var CState2 = document.getElementById(subclass2);
            if (CState1.style.display != "none") {
                CState2.style.display = "block";
                CState1.style.display = "none";
            }
            else
            {
                CState2.style.display = "none";
                CState1.style.display = "block";
            }