Attempting to upload a file using Opera throws a Javascript error (6.22 version)

Attempting to upload a file using Opera 11.51 throws a Javascript error of "An HTTP error 0 occurred.
/upload/js". If you hit okay on the error pop-up and submit your content, it ends up creating a page that shows a whole bunch of file text (for instance, text that you would see if you opened a PDF in a NotePad). I have had this problem for years, but I thought it was isolated to my site, but two or three other 6.22 sites have it as well.