[Guy Harris <guy@xxxxxxxxxx>]

> I'm trying to write a program based on mergecap, and I keep getting that
> error.  Could someone point me in the right direction on what could cause
> such an error to occur?

What can cause it to occur is an attempt to write, in a particular
capture file format (e.g. libpcap, or Network Monitor, or Sniffer,
or...), a capture of a particular link-layer network type (e.g.,
Ethernet, or Token Ring, or X.25, or...) when either

	1) that capture file format doesn't support captures of that
	   link-layer type (e.g., X.25 in libpcap)

or

	2) it does support captures of that link-layer type, but the
	   Wiretap library doesn't have code to write captures of that
	   link-layer type in that capture file format (because it
	   hasn't been written, either because, in turn, nobody's had
	   the time to write it, or because we don't know how to write
	   out captures in that format for that link-layer type).