processListFile
The file name may be empty, there may have been a list file parsing error, the filename may have an unsupported extension, or the file may have failed various checks (for example, it does not exist or cannot be opened for reading, or the file is empty).
Inspect the contents of the list file using a text file editor to make sure that each entry has the correct syntax (see line format). Take the name of each of the listed files in turn and check that it has a valid filename extension, that the file actually exists, that it is not empty and that it has read access permissions set.