For a picture I want to upload on last version of Discourse, max_image_size_kb and max_attachment_size_kb both at 4096, event if I set 20000 Kb, my picture (jpg) is 1.2Mo and I have this error:
Sorry, this file is too large (the maximum size allowed is 4096 KB).
Unless you can reproduce it here, this is a configuration problem with your instance. 4MB is the default upload limit in Discourse.
The most common cause of this issue is a reverse proxy that is not configured properly.
I had exactly the same problem, but setting client_max_body_size in my reverse proxy fixed this.
But the error message displayed is misleading, because it tells the user the value set in max_image_size_kb and not the setting that is causing the problem. Maybe this could be changed to a better wording.
同样的情况也发生在我身上，错误消息只会让人更加困惑，而不是提供帮助。请改进错误消息，使其更具可操作性。
对不起，该文件太大了（最大尺寸为 50 MB）。为什么不将大文件上传到云共享服务，然后粘贴链接？
……而我上传的文件在 10 到 20 MB 之间。
@meglio，我们最近也遇到了同样的问题，您是否找到了解决方案？