It seems not a Rebol error. The program I wrote make a preview of PDF files, so I call external software, and probably is the external software that send the error message. To make a preview of a pdf in Linux do: Code: call/wait "pdftoppm filename -f 1 -l 1 -scale-to 50" call/wait "ppmtojpeg filename-1.ppm > filename.jpg" The error is about pdf. The same error appears in pdf viewer evince wiht other users...