Earlier versions don't work. The current version 4.x is a big improvement. Since some of the files are quite large you may have a problem with the server timing out if you are on a slow connection. Try downloading the file at a time when the connection is less busy. Some printers can't do PDF files for reasons known only to the people who sell them.
Memory can be a problem for some printers on some large files.
Let the Webmaster know if none of these things helps. On two occasions, one recently, our ISP has changed its settings or had a bug in a software patch which prevented downloading our PDF files. You may be the first to discover the problem. If not, use our Comment Form . Your comment will be directed appropriately.