The file system of your operating system may have gotten out of sync with IRIS. Try clicking View->Refresh while in the File Browser application.

Or, the file could have been moved outside of the IRIS File Browser. Currently, if a file has been harvested and then it is moved to a different location in the file system using another tool besides the IRIS File Browser such as Windows Explorer, IRIS will not be able to find it. In the File Browser Application, find the file in its new location and, with the file selected, re-establish any connections the file has with other data items using the Connections Pane in the Sidebar->Connections and Suggestions pane. You may end up with more than one connection to the file in the data item you choose to connect to the file. This also can't be remedied currently.