If you try to add an attachment to a bug and it doesn't work because you don't specify a file name, or the file name you specify doesn't exist, or you don't fill in the description, you get an error telling you to hit the Back button and try again, but at least in Netscape 4.73 that doesn't work. When you hit the back button, you see the same error again, and then when you hit the back button again, it takes you back to the bug. The first time you hit the back button should take you back to the create-an-attachment page.
Ok i have changed the behavior for this. It should now print a different error message that will allow you to return without error. Let me know if this did not solve the problem for you.
I don't think this fix is adequate. If I use the "attach" link you've added, then the information I previously put in the attachment information fields is lost. The correct behavior would be for the Back button to work properly as the previous error message suggested. Why can't it be made to work?