ISOLatin1Encoding has something to do with the way images or fonts are encoded in a PostScript file. It is not really a generic error code, which is good because it means this error can easily be pin pointed.

A PostScript error "undefined", offending command "ISOLatin1Encoding" can indicate that you are printing a PostScript level 2 file to a PostScript level 1 device.Check your settings and try printing again.

The error can be caused by a bug in certain printer drivers, even if they know you have a level 1 printer. Switch drivers if all your settings appear to be correct.

I also read once that this error can show up in TrapWise 2.X when the Windows driver is set to download TrueType fonts as Type42. TrapWise cannot handle Type 42 fonts because it does not have a built in TrueType rasterizer. To solve this error, check the font settings in the PostScript driver and set the "send TT fonts as" to "outlines" instead of "Type42".

TrapWise 2.X will also generate this error if the PostScript file it tries to trap contains JPEG compressed images.

And TrapWise can also generate this error if you print PageMaker files on PC using recent versions of the Adobe PostScript driver. Using version 4.1.x to create PostScript should solve the problem.