How To Stream An Excel 2007 Or Word 2007 File Using C#

I'm working on a web app and need to stream various files. I can do pdfs, images, and older Office documents. However, when I try to do with 2007 documents, it breaks. Here is my code:

Response.Buffer = true;
Response.Clear();
Response.ClearContent();
Response.ClearHeaders();
switch (FileExtension.ToLower())
{
case "pdf":
Response.ContentType = "application/pdf";
break;
case "doc":
Response.ContentType = "application/msword";
break;
case "docx":
Response.ContentType = "application/vnd.ms-word.document.12";
break;
case "xls":
Response.ContentType = "application/vnd.ms-excel";
break;
case "xlsx":
Response.ContentType = "application/vnd.ms-excel.12";
break;
default:
Response.ContentType = "image/jpeg";
break;
}
Response.BinaryWrite(buffer);

The error that I get is:

An invalid character was found in text content. Error processing resource 'http://DomainName/GetFile.aspx.