Sounds like a misdirected error message, maybe. Are you sure the file was created by someone with the same version of Creo that you are trying to use to read it? There's a tendency with releases of Creo to not have files be backward compatible (i.e. a part created in Creo 4.0 might not be readable by Creo 3.0). Maybe that's the case and the error message is just not correct?
Alternatively, was the file "transferred" or otherwise altered on a Unix based system? For example, Mac OS X is based upon Unix, or maybe Linux? Is the file actually binary or non-binary? Text files from Windows and Unix-based operating systems differ in the characters they use to designate end-of-line and line-feed.
Since there aren't any versions of Creo that I know of that will run on a Unix-based operating system (that ended back in the Pro/Engineer days), it can't be that a person was able to make the file on such a system...
