TL;DR

Fix the codeigniter plupload upload problem of  “You did not select a file to upload.”  by making sure that you pass the correct file array key to do upload:

$this->upload->do_upload('file');

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How I found it:

I’ve been working on my first codeigniter project that required me to upload some images. For that task I chose Plupload. A super slick upload manager written by the same people that brought us tinymce.
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