Server Error while adding multiple items

In my case it's an ISS issue, If your running your project in IIS express in VS 2013 like mine try changing this

<script type="text/javascript" src="../App_Themes/Default/jquery1_7.js"> </script>

<script src="../js/RadWindowMethods.js" type="text/javascript"></script>

<script src="../js/OpenStatusPopup.js" type="text/javascript"></script>

<link rel="stylesheet" href="../RupeesFont/RupeeForadianStylesheet.css" type="text/css"

To This, change (../) to tilde(~/)

<script type="text/javascript" src="~/App_Themes/Default/jquery1_7.js"> </script>

<script src="~/js/RadWindowMethods.js" type="text/javascript"></script>

<script src="~/js/OpenStatusPopup.js" type="text/javascript"></script>

<link rel="stylesheet" href="~/RupeesFont/RupeeForadianStylesheet.css" type="text/css" 

My reference :

https://msdn.microsoft.com/en-us/library/58wxa9w5.aspx