By default (when packet-size is not specified), the size of transmitted packets is 64 bytes. The minimum value allowed for packet-size is 8 bytes, and the maximum value is 4095 bytes, on some systems is even 65000. If packet-size is smaller than 16 bytes, there is not enough room for timing information. In that case, the round-trip times are not displayed. In your case, the -n flag probably means something else, not the count number.]
The error number looks like AIX, I just tested AIX, and I seem to be right : -n flag means "packet-size", as well as "-s" whereas the count is "-c" flag.