IValidate interface for multiple pagetypes

Hi All,

I am new to EPiServer. I am using IValidate interface for validating the default property of episerver page i.e CategoryList. I would like to restrict the count of category selection for example say only one category should be selected. I did this for a single pagetype, But i am getting the following exception , while adding additional page types,"Ambiguous match found". It may be simple one i may not know. I have attached my code below.

public class BasePageValidator : IValidate,IValidate
    {        
        IEnumerable IValidate.Validate(SamplePage page)
        {           
            if (page != null && page.Category.Count > 1)
            {
                return new[] 
                 { 
                    new ValidationError() 
                    { 
                       ErrorMessage = "Field IntroText cannot be empty!", 
                       PropertyName = page.GetPropertyName(pg => pg.Category),
                       Severity = ValidationErrorSeverity.Warning, 
                       ValidationType = ValidationErrorType.AttributeMatched
                    } 
                 };
            }
            return Enumerable.Empty();;
        }
        IEnumerable IValidate.Validate(Products page)
        {            
           return Enumerable.Empty();
        }
    }

It is not working after adding "IValidate", getting an exception.

I need to set this restriction for some pagetypes more than one. Suggest me on how to achive this one.

Thanks in advance.