To reproduce:
- Enable the paging and add 1000 rows.
- Press Ctrl + End
- An exception is thrown.

Workaround:

radVirtualGrid1.VirtualGridElement.InputBehavior = new MyBehavior(radVirtualGrid1.VirtualGridElement);

class MyBehavior : VirtualGridInputBehavior
{
    public MyBehavior(RadVirtualGridElement element) : base(element)
    {

    }
    protected override bool HandleEndKey(KeyEventArgs keys)
    {
        this.GridElement.PageIndex = this.GridElement.TotalPages - 1;
      
        return true;
        //return base.HandleEndKey(keys);
    }
}