I created a simple sample based on your information.

I was unable to repro the horizontal scrollbar issue on my sample. Please make any necessary changes to the sample and then have the sample send back to us for further investigation.

I have tested yours, it works fine with other browsers except IE 8 compatibliity view .  In IE8, without compatibility view no horizontal bar comes, but the headers are not aligned properly. In compatibliity view, the headers are aligned properly but the horizontal bar comes even if i set the width to 100%. I have attached the sample project that i have tested. please check in IE8 compatibbilty view.

One more thing what i needed is, if i have set the height of the grid to 200 and  the first six records got loaded a vertical scroll bar should be appeared if more than 6 records found. The idea of clicking "Load more data" is good but not all the end users will know that.

We don’t recommend you to use IE8 in compatibility view mode because it will cause improper rendering by the IE itself. It will also bring several old issues back in IE.

One more thing what i needed is, if i have set the height of the grid to 200 and  the first six records got loaded a vertical scroll bar should be appeared if more than 6 records found. The idea of clicking "Load more data" is good but not all the end users will know that.

The appearance of vertical scrollbar is automatic. When the content is bigger (in this case is height) than its container, thus the scrollbar will appear. And vice versa. I think it's default behavior of scrollbar.

Thank you for your valuable feedback of VirtualPaging UI. Do you have any recommendation about how the "Load More Data" UI so that end users will notice that?

For "Load more data" option, if the page size is 6 and if it contains more than 6 in the datasource then we can enable the vertical scroll bar. That will intimate the end user that more than 6 records are present.

In IE8 without compatibility mode, the grid headers are not aligned properly.