I realise now what I was doing wrong. I had previously forked
node-red-contrib-owfs in order to do some enhancements to it. To use
the forked version I linked
/usr/lib/node_modules/node-red-contrib-owfs to my fork. In order to
update the node I had fetched the latest version from the authors
repository and had not realised that I needed to include a copy of
bluebird inside the owfs node directory. I have now done the job
properly(?) by updating the node via npm, copying bluebird across to
my fork, and relinking the directory to mine.
I will get the hang of how this all hangs together eventually. Sorry
for the noise
Colin