These ".DS_Store" files are system generated by your mac computer (I think it's used to index files for spotlight searches). The file is also hidden.
Arc, however, does not filter system files - it just looks in the directory, finds the list of all files and tries to load them... and of course the news.arc tries to convert all the file names into integer keys (when loading into a table), but ".DS_Store" can not be coerced to an int, so instead you get that error.
You can fix this one of two ways. You can hack the OS to stop auto generating these files or you can change the code that gets the list of files and filter out that system file.
