Error '.xls' is in a different format than specified by the file extension

[admin]

I found a plugin that helps me export ExtJS grid data into MS Excel sheet.
<a href="http://druckit.wordpress.com/2013/10/26/generate-an-excel-file-from-an-ext-js-4-grid/" rel="nofollow noreferrer">http://druckit.wordpress.com/2013/10/26/generate-an-excel-file-from-an-ext-js-4-grid/</a>

all works great except for the error I'm getting before opening the file.

<img src="

https://imgur.com/TvNtT

" alt="enter image description here">

Peace of my code:

if (Ext.isChrome || Ext.isGecko) { // local download
            var gridEl = this.getEl();

            var el = Ext.DomHelper.append(gridEl, {
                tag: "a",
               download: title + "-" + Ext.Date.format(new Date(), 'Y-m-d') + '.xls',
               href: location
            });

            el.click();

            Ext.fly(el).destroy();

        }

One solution suggested that i remove the apostrophe so i tried:

download: title + "-" + Ext.Date.format(new Date(), "Y-m-d") + ".xls",

But no luck. Any idea?