Where exactly is it leaking from? Is it in an area where it looks like
flashing or is it an area that looks like it's leaking from the actual
My bet is that the contractor did not correctly install the flashing.
Also, not sure what exactly "tighening up the flashing" means. Either
the flashing is installed correctly or it isn't. Who did the install?
Do they have good references and experience doing skylights?
Have you tried talking to Velux (1-866-358-3589)? On a new install,
especily if the contractor used a Velux flashing kit, they they may be
willing to send out a tech rep to take a look w/o charge.