>>17035617...No, nil isn't the name of the file. nil is programming lingo for "non-existent". It means the variable "filename" has no value. I took a look at the script SpriteWindow line 218, and it's just an error handler.
What it means is that there's a file missing somewhere. The problem is I don't know where. I extracted everything so nothing should be missing. Has the rar been changed at all since it's been uploaded?