Hi Ken, Ted,
I tried Ted's file on my IrfanView (IV for short) installations. I have most of the versions reaching back to 2005 in parallel on my WinXP.
The file opens ok on IV 4.32 and previous versions; it opens too dark on IV 4.33; it doesn't open on the current IV 4.35.
I also downloaded some .X3F files from another site (http://www.rytterfalk.com/) - none of them opens in any IV version, in some the embedded previews open.
BTW: when testing make sure the option for displaying the embedded previews/half size images is turned off, so you don't mistake them for the real thing
The bottom line is, I think, that the FORMATS.DLL after IV 4.32 has a bug.
Cheers,
Frank