My NAV4 has output a large printout entitled...

The NAV4 buffer fault report is a standard report produced by the NAV4 if the print buffer overflows. This is not a fatal error report and you have no need to worry. The buffer fault report indicates that your NAV4 has noticed a printing error when recalling a NAVTEX message from memory.

This type of report is however rather unusual, if a GPS or instrument system is connected it could also be related to the amount of NMEA data sent to the NAV4.