Here is a great article that tells you how to resolve documents that are stuck in the Microsoft Office Document Cache (Uploader) when it is convinced that you have a document in there to upload that doesn't exist.

http://office.microsoft.com/en-us/excel-help/manually-rename-the-office-document-cache-HA101848838.aspx

• Close all Office programs.
• Click the Ctrl + Shift + Esc keys to open the Task Manager.
• On the Processes tab, select MSOSYNC.EXE, click End Process, and then close the Task Manager.
• Navigate to %userprofile% \AppData\Local\Microsoft\Office\14.0\ in Microsoft Office 2010 or %userprofile% \AppData\Local\Microsoft\Office\15.0\ in Microsoft Office.
• Rename or delete the OfficeFileCache folder.