The software is transferring files. The file is finished transferring when the progress bar fills up.
When the software transfers file sets, two progress bars appear. The top bar shows the progress of single files in the set, and the bottom bar shows the progress of the file set. The file set is finished transferring when the bottom progress bar fills up.
You may see this dialog box when submitting files to a hot folder in the Controller Viewer or when opening files in the High Resolution Sheet Viewer.
 | Wait for the progress bar to fill up. |