Sounds very much like the registry settings may have been edited - perhaps with a support ticket or similar. That sounds suspiciously like the option to read all rows in a column to determine its type. Otherwise, your package could be treating that column as just about any other type and running into issues w/ conversion.

I assume that you've verified for all of the non-NULL columns that the data contains a valid date and not something that's almost a date. Is it possible that it's trying to read in some slightly different format for the date and choking on that? Perhaps trying to read dd-mm-yyyy instead of mm-dd-yyyy or yyyymmdd?

Without knowing too much more about the file(s), is it also possible that the files that have run successfully have had fully populated date columns? I know that once you release a spec into the wild you don't really know what you'll get back.