Wow. That’s one hell of a bug. It looks like it’s trying to render the sky texture onto the sails in a project from view set up - see the sail below the horizon line. That proves the sails are not just invisible. Egad…
Sorry, can’t help! This might be something to post on the main blender site, if you can find the bug…
Hmm, you’re sure you didn’t accidentally move those objects to the mask layer or something?
That sail issue is very odd. Do the sails have any thickness to them? If it is a bug you might try extruding them a little and see if it that helps. I have run into several lighting issues that were fixed that way.
Its actually something I’m saving for a later date to do some experimenting with, just creating a new material fixes the result.
I can see it being very useful if its applied to a cloth… instant invisibility cloak, wondering if it will also be useful for the next blender movie in occluding geometry you dont want to be seen
Hi,
Nice ship 
Did you lower the sails material alpha to make them transparent ? If so you also need to activate ztransp to see what’s behind them … otherwise the renderer patches directly to the sky texture.
Cheers,
Holy censored it’s a crazy bug but a great looking W.I.P. IMHO!
Thanks for the comments everyone.
Been doing some ship rigging, and working out where the ropes go, then added some lense flare and changed the composition… thinking of having a hand reach out to the ship…
Boy am I glad I didn’t pick something complicated… this ships rigging is driving me nuts, Also tried to add some cloud but got some very nasty artifacting, so gave up on that 
using the soft body dynamics for the sails, diddnt like the results using the cloth… hmmm I’m just going bitch bitch bitch arent I? need sleep, it will all be OK tomorrow
Another quick update, lightened it up a but
Nice modeling
hmmm seems like the waves need to be changed in some way as it looks like the boat is a toy in a puddle
but other wise very very nice