Help - error converting to fax format

[Mark Lehrer <mark@lehrer.nlcomm.com>]

Could someone give me a quick hint on what to check here?  This was
emailed to me by the fax daemon, but it makes no sense to me (yet 8^)

Thanks!!!  Text follows:


Your facsimile job to 12165554308 was not sent because document conversion
to facsimile failed.  The output from the converter program was:

Error: /invalidfont in findfont
Operand stack:
   Helvetica-Bold   15364   --nostringval--   Helvetica-Bold   NimbusSanL-Bold  
 Helvetica-Bold   NimbusSanL-Bold
Execution stack:
...