Reliability Of HTTP Get Of ASP Page

I have an app that gets a file from a web server. An ASP page is passed authenitication data (username, password) and a filename. The file is read and then output by the ASP page so the only response is the file I am requesting. The file I want to receive is XML with the major portion of it being a Base64-encoded block.

I use the Indy component TidHTTP to get the file:

HTTPClient.Request.ContentType := 'text/html';
HTTPClient.Request.CacheControl := 'no-cache' ;
Response.Text := HTTPClient.Get (TIdURI.URLEncode (URL)) ;

Problem is that more often than not, the returned file contains errors. In a 200k file, 2 or 3 characters are often munged. Occasionally I manage to receive the file without errors. Code: