It looks like you've specified the printer command with quotes around
it, perhaps, where quotes are not expected, and the whole string is
being treated as a long filename with spaces in it, rather than as the
name of a command with trailing options.... i.e. it's actually trying
to find and run a file called
"/usr/local/bin/flpr -hfnprt.fnal.gov -qwh3e_hp5si_d:"
rather than trying to find /usr/local/bin/flpr and run it with the
supplied arguments.
If it were "flpr" that were not being found the error message would
say
sh: /usr/local/bin/flpr: No such file or directory
Hope this helps.