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In some situations, most commonly when updating to a new version, Final Cut Pro X can forget export settings. This can result in the Open With action of the export preset being reset to Do Nothing. This means that when selecting Share > Send to Kollaborate, after FCPX has finished rendering the file does not get sent to the helper and therefore does not upload.
To fix this, go to Share > Send to Kollaborate then click on the Settings tab. Set Open With to "Kollaborate FCPX Exporter". If the app is not already listed in the dropdown menu you can find it in the /Applications/Digital Rebellion folder.