Assign an Excel file to a File Input object. connect the File input to a Workspace. Click on the workspace object, in the workspace property expand the load plans, in the File Name pick list you should see the original path and excel file name as well as the name of the File Name object. Select the File Name object's name.
You should also see the change list history in the workspace properties page.
In the following screenshot the File input name is TextFiles, but the workspace in dataprep was configured to process 2006.txt file.
If Mo's Suggestion does not resolve the issue, it could be a permission problem; especially if the new report is in a different location to your original report.
Are you able to place the file in the same location as the original for testing? If that works, then please check that the domain account being used to run the Agent service on the Datawatch Automator server has access to your new file location.
Additionally, if the file is in use (in Excel from your desktop, for example), the process will fail.