C# - Store Files In ASP Website Then Download To Browser

I'm creating an Excel file in C# on my asp.net web site. Then, I want to save this file somewhere within the web server's files, and send that file to the browser for the user to download. I've got it working on my local system in the dev environment, but I'm not getting the file addressing right. How can I store a file in "~ParentFolderSubFolderfile.ext". Then send that file to the browser for user download.

String outputFile = Utilities.writeToExcelFile("", MapPath(@"~ReportFilesTempFilesDropShipData.xls"), table);
DownloadFile(outputFile);
public void DownloadFile(string fname)
{
string path = fname;
string name = Path.GetFileName(path);
string ext = Path.GetExtension(path);
string type = "";
// set known types based on file extension
if (ext != null)
{
switch (ext.ToLower())
{
case ".htm":
case ".html":
case ".aspx":
case ".asp":
type = "text/HTML";
break;
case ".xls":
case ".xlsx":
case ".csv":
type = "Application/x-msexcel";
break;
case ".pdf":
type = "Application/pdf";
break;
case ".txt":
type = "text/plain";
break;
case ".doc":
case ".docx":
case ".rtf":
type = "Application/msword";
break;
}
}
Response.AppendHeader("content-disposition",
"attachment; filename=" + name);
if (type != "")
Response.ContentType = type;
Response.WriteFile(path);
Response.End();
}

Again, this works fine on my local pc, but when I move it to the server I get an error for accessing the path. And the path listed in the error code is NOT where I want the file to go.