edit uploaded file/image

[jetsekoopmans]

I upload a file with the following:
@post = Post.first()
result = Post.upload(uploaded_file.tempfile, uploaded_file.original_filename, content_type: uploaded_file.content_type)
@post.thumbnail = {"name" => result["name"], "__type" => "File", "url" => result["url"]}

When I want to edit this file I use the same code but I get the following error:
IOError at /posts
closed stream