this is one area that the iSeries is not so foolproof. For example, Query/400 can put a *MDY field on a report. But, try to output the field to a data base file; it goes out as a L date field, but is 8 long. You get IO errors when reading.
This is almost the same problem. I suggest that you keep all date values in ISO format in data files. For displays, use a 8 or 10 character field and not type L.
Your problem is that the L type field is not consistent with the *MDY just like the Query/400 example above. Change to a character field.