Asp custom validator is not working in IE-11

<asp:DropDownList ID="cboType" onChange="fnInvalid(this,'hidTypeValid');getSelectedValue('cboType','hidliab');changeOptions(document.forms[0].hidliab,document.forms[0].cmbLiability,document.forms[0].hid_liab,document.forms[0].HIDSERLIAB);" runat="server" name="cbotype"AutoPostBack="true">
</asp:DropDownList>
                                                            <asp:RequiredFieldValidator ID="VreqvalidateType" runat="server" Display="None" ControlToValidate="cboType" ErrorMessage="-Case Type should not be blank" InitialValue="Choose"></asp:RequiredFieldValidator>

<asp:CustomValidator ClientValidationFunction="fnInvalidSelection" ID="VcustTypeValid"
runat="server" Display="None" ControlToValidate="cboType" ErrorMessage="-Case Type should have valid selection."></asp:CustomValidator>

<asp:CustomValidator ClientValidationFunction="fnTypeFileClass" ID="VcusTypeFile"
 runat="server" Display="None" ControlToValidate="cboType" ErrorMessage="- Case File Classification should not be empty."></asp:CustomValidator>

 <asp:CustomValidator Enabled="false" ClientValidationFunction="fnTypeCaseHandler"
  ID="VcusTypeCaseHandler" runat="server" Display="None" ControlToValidate="cboType"
  ErrorMessage="- Case Handler 1  should not be empty."></asp:CustomValidator>

<pre lang="C#">function fnTypeCaseHandler(sender,args)
		{
		var s = args.Value;
		args.IsValid = true;
			if (s!="K")
			{
			var handler1= document.frmCaseDetails.cmbHandler1.value;
			if (handler1 =="Choose")
			{
				args.IsValid = false;
			}
			}
		return args.IsValid;
		}

function fnTypeFileClass(sender,args)
		{
		var s = args.Value;
		args.IsValid = true;
			if (s!="K")
			{
			var file = document.frmCaseDetails.cmbFileClass.value;
			if (file =="Choose")
			{
				args.IsValid = false;
			}
			}
		return args.IsValid;
		}