GPL Ghostscript 8.63: Unrecoverable error, exit code 1

[Wolfgang Engelmann]

By running lyx1.6.1 under debian lenny I get this message repeatedly:
GPL Ghostscript 8.63: Unrecoverable error, exit code 1
it is apparently not preventing a pdf output of my book, but would like to 
know the cause of the message and a cure

Wolfgang