An "Error 401" message when attempting to sync your files with Dropbox typically occurs when there is a permissions issue preventing Pixlmob from accessing the folder you've designated to sync the files.

[Note: this involves the permissions for the integration, not the permissions for the folder itself.]

To resolve this error, you should disconnect your Dropbox integration from the integrations tab of your Pixlmob account and then reconnect it. Once it has reconnected, you can follow the steps to sync the images to your Dropbox folder.