FAT file systems have a limitation when it comes to naming conventions. You must use the 8.3 format, so that file names look like “NAME001.EXT”, where “NAME001” is an 8 character or fewer string, and “EXT” is a 3 character extension. People commonly use the extensions .TXT and .LOG. It is possible to have a shorter file name (for example, mydata.txt, or time.log), but you cannot use longer file names. Read more on the 8.3 convention.