ie7 creating problem with cache

Question

Hi all,

I've use cache in my code,and after that ie7 is giving js error pop-up which shows "there was a problem while using xmlhttp; not found"

The page is running fine on Firefox,

Any idea what makes it there in ie7?

this is the code

DataSet dsProduct = null;
        Double CachingHrs = Convert.ToDouble(ConfigurationManager.AppSettings["DataCachingHours"]);

        if (ProductListURL != string.Empty && ProductListURL == URLParameterValues.PRODUCTLIST)//If URL call is for Product list
        {
            if (null != Cache[ProductListURL])
                dsProduct = (DataSet)Cache[ProductListURL];
            else
            {
                dsProduct = DataModel.SubCategoryHelper.getProductList(SiteManager.GetSiteTextCode(), SiteManager.GetAppSiteCode().ToString());
                if (dsProduct.Tables[0].Rows.Count > 0)
                    Cache.Insert(ProductListURL, dsProduct, null, DateTime.Now.AddHours(CachingHrs), TimeSpan.Zero);
            }

        }

If I remove caching part,there is no error.

Plz let me know if you need more information.

Any help appreciated .

Thanks in advance