This note is for Emacs 23 on Windows XP.

Within Emacs I got the following error message when trying to open a file using Ctrl-x Ctrl-f:

Format specifier doesn't match argument type

The problem was in the file name, which was too long. Windows XP file names may be 255 characters long, which should be enough. The problem with Windows XP is that the same restriction also applies to the full path name. So the length of the file name plus all directory names must no exceed 255 characters either.

I could not copy the file to the directory with the long name using Windows Explorer in the first place, and instead I had copied the file with Cygwin. After shortening some directory names I was able to properly copy the file and open it within Emacs.