The caching system has been changed today to stop the annoying "back button not working" problem. As a result file links should now be changed to ensure better user interaction (as well as stopping the 404 error occuring when your page hasn't been cached!).
If you currently use the "http://www.tessource.net/files/cache/fileid.html" system to link to your file you can easily change it by taking the fileid (NOT the .html part) and changing the link to "http://www.tessource.net/files/file.php?id=fileid".
While your cache links will still work I'd recommend changing your links whenever possible.