Is the prefix always the same? And will there always be just one file with that naming convention in that location at any given time?
If so, I would create a context parameter with your file path, remembering to escape the slash, and another one for your file name, setting it as "[prefix]*.[extension]". Then you can put the file path parameter in the Directory portion of tFileList and the file name in the Files section.
If not, I would need more information before I could advise you.
