If nothing has changed on the system, then keep looking in the source file... the problem is there and you've just not seen it yet. My favorite error is when they use a "text qualifier" as part of a name or something. For example...

"Jackson, Andrew "Stonewall"",123,456,"some other info"

See the error? They've included a nick name in the first field and decided to use the text qualifier character of (") to indicate the nick name.