In some contexts, Moodle blocks file uploading, therefore disabling filepicker (or the Nanogong button in TinyMCE in you have that filter installed).
Examples of such contexts:
- comments to an answer in a quiz (mod/quiz/comment.php)
- grade editing page (grade/edit/tree/grade.php).
Is there a way to circumvent this restriction to allow file upload form the text editor in any context ?