Custom Validation for Checkbox in MVC Razor

public class RegistrationModel { 
[Required(ErrorMessage = "Please Enter Email Address")] 
[RegularExpression(".+@.+\\..+", ErrorMessage = "Please Enter Correct Email Address")] 
public string UserName { get; set; }
[Required(ErrorMessage = "Please Enter Address")] 
[Display(Name = "Address")] 
public string Address { get; set; }
 // Applying Custom Attribute 
[MustBeTrue(ErrorMessage = "Please Accept the Terms & Conditions")] 
public bool TermsAccepted { get; set; } }
 //Making Custom attribute for validating checkbox 
// IClientValidatable for client side Validation
public class MustBeTrueAttribute : ValidationAttribute, IClientValidatable 
{ 
public override bool IsValid(object value) 
{ 
return value is bool && (bool)value; 
}
 // Implement IClientValidatable for client side Validation 
public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
 {
 return new ModelClientValidationRule[] {
 new ModelClientValidationRule { ValidationType = "checkboxtrue", ErrorMessage = this.ErrorMessage } };
 } 
} 

 @model Mvc4_Model_ServerSideValidation.Models.RegistrationModel
@{ 
ViewBag.Title = "Validating CheckBox";
}
<script src="../../Scripts/jquery-1.7.1.min.js" type="text/javascript"></script>
<script src="../../Scripts/jquery.validate.min.js" type="text/javascript"></script>
<script src="../../Scripts/jquery.validate.unobtrusive.min.js" type="text/javascript"></script>
<script type="text/jscript">
 //Custom jQuery validation unobtrusive script and adapters 
jQuery.validator.unobtrusive.adapters.add("checkboxtrue", function (options) 
{ 
if (options.element.tagName.toUpperCase() == "INPUT" && options.element.type.toUpperCase() == "CHECKBOX")
 {
 options.rules["required"] = true;
 if (options.message) {
 options.messages["required"] = options.message;
 }
 }
 }); </script>
<h2>Custom Validation for CheckBox </h2>
@using (Html.BeginForm())
{
 <fieldset> 
<legend>Custom Validation for Cascading Dropdown List</legend> 
<ol> 
<li> 
@Html.LabelFor(m => m.UserName) 
@Html.TextBoxFor(m => m.UserName, new { maxlength = 50 }) 
@Html.ValidationMessageFor(m => m.UserName) 
</li> 
<li> 
@Html.LabelFor(m => m.Address) 
@Html.TextAreaFor(m => m.Address, new { maxlength = 200 }) 
@Html.ValidationMessageFor(m => m.Address) 
</li> 
<li> 
@Html.CheckBoxFor(m => m.TermsAccepted)
@Html.ValidationMessageFor(m => m.TermsAccepted) 
</li> 
</ol> 
<input type="submit" value="Submit" /> 
</fieldset>
 }