X is not a constructor in nodejs

I'm programming a flow in node-red, now i'm getting this error inside a node function:

var PromiseFtp = global.get('promiseFTP');
var fs = global.get('fs');
var ftp = new PromiseFtp();
var fileToGetAndDelete = 'file.xls';

 ftp.connect({host: 'server', user: 'user', password: 'password'})
  .then(function (serverMessage) {
    return ftp.get('/foo/foo1/'+fileToGetAndDelete);
  }).then(function (stream) {
    return new Promise(function (resolve, reject) {
      stream.once('close', resolve);
      stream.once('error', reject);
      stream.pipe(fs.createWriteStream('foo.xls'));
      ftp.delete('/foo/foo1/'+fileToGetAndDelete);
    });
  }).then(function () {
    return ftp.end();
  });

error:

"TypeError: PromiseFtp is not a constructor"

what's wrong?

thanks in advance.

via OiRc