Doubt related with Returnurl

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C#

Hi all

Im redirecting pages to index.aspx page which is inside a folder employee and the url is www.abc.com/hrms/employee/index.aspx.and my home page is in hr folder hr.aspx problem is when redirecting url with querystring return url

if (Request.QueryString["ReturnUrl"] == null)
{
    returnUrl = "~/hr/hr.aspx"
}
else
{
    returnUrl = Request.QueryString["ReturnUrl"];
}
Response.Redirect(returnUrl);

im using this code.but else part leads to exception return url concatenates with abc folder like www.abc.com/hrms/employee/returnurl instead i want www.abc.com/hrms/returnurl .
if my return url with querysting is like this
www.abc.com/hrms/employee/index.aspx?Returnurl=hr/bonus.aspx" when login error arising with the code given above url redirects to www.abc.com/hrms/employee/hr/bonus.aspx but i want this to direct to www.abc.com/hrms/hr/bonus.aspx

why happening so? How to overcome this

Thanks in Advance
Amrutha