Files in /dev are special files creaked by the mknod command (IE when MAKEDEV is run, or I think udev does it on demands in some cases).
Anyway - it is not something to worry about, it just means that for whatever reason, that device node wasn't created.
I had a similar issue in Debian - they would only create /dev/ttyS0 through /dev/ttyS3 but my modem was on a pci card, and was /dev/ttyS4. So I had to make the node myself. Happens sometimes, udev is suppose to make it a little bit better.