By default a converter PNG->EPS is defined. Since I defined an EPS->PS converter, Lyx then converted PNG->EPS->PS and failed to load the image (see previous message). So I removed the PNG->EPS converter, so that the PNG->XPM get used. However, the images still didn't get loaded. "lyx -dbg graphics" shows that lyx converts PNG->XPM->EPS->PS! Lyx _can_ load xpm directly and does so, if I delete the EPS->PS converter. This is minor once one knows what happens. There are always ways to work around this, defining only the right converters. But it still seems odd.
Jan PS : This has been verified using lyx1.2.1cvs as of june 22 on Solaris(sparc) 2.7, xforms 0.89.6 and Image Magick 5.4.5.