Server.Mappath not finding root properly

My code is running in ASP.Net MVC and I have created a custom ActionResult, in it I have the following overload:

public override void ExecuteResult(ControllerContext context)
{
if (!String.IsNullOrEmpty(FileDownloadName))
{
context.HttpContext.Response.AddHeader("content-disposition", "attachment; filename=" + FileDownloadName);
}

string filePath = context.HttpContext.Server.MapPath(VirtualPath);
context.HttpContext.Response.TransmitFile(filePath );
}

and this is all fine from VS 2008.
So, I published this only to find that when I try to click the link on the host I get the following:

Could not find a part of the path 'E:\web\<my discount.asp username>\htdocs\<virtual path>

(paths missing for security)

this is very urgent

 

Where is this file? Is it directly under the root or is it inside some subdirectory?