Well, I spoke too soon. There is an issue with Alfresco 1.4 requiring a Servlet 2.4 environment. I commented out the 2.4 call and replaced it with a 2.3 compatible call. I can now download files!
To make this run in 6.1 you need to change the following web-client.jar file as follows:
1 - make a backup copy of web-client.jar
2 - get the source code (or disassemble) for BaseDownloadContentServlet.class in package org.alfresco.web.app.servlet
3 - change the following code at line (or around) line 243
// set mimetype for the content and the character encoding for the stream
res.setContentType(mimetype);
String encoding= req.getContentType() +"; charset=UTF-8";
res.setContentType(encoding);
// res.setCharacterEncoding(reader.getEncoding());
4 - recompile the changed class
5 - add the new class file to the web-client.jar (ensure you have replaced the proper file!)
6 - restart the web server
Now you can download files without exception! This may or may not work in your environment, but it "works for me".
E/.