In their web site they say that they own rights to the publishing of the building at night, because they hold the copyright of the lighting scheme. IIRC they don't even mention commercial use, they just claim money for any kind of publication.
I wrote to them twice (once in English, once in French) stating that I am a professional photographer, that I do sell images of the Eiffel tower at night, that I have no intention to recognize any rights whatsoever to them unless they state the norms which would support their claims, and I received no answer in both cases.
If you are prepared to pay, they do take the money. If you ask why should you pay, they don't answer. I do encourage everybody to ask similar questions to them.
It's urban myth that you cannot take pictures of certain buildings because they are "copyrighted" (the Sidney Opera Theatre etc.). Yes you cannot use the picture commercially because the image of the building is tied to the organization linked to it, but that's true also for the theatre in Bayreuth or the Teatro dell'Opera di Roma or La Scala in Milan or whatever other Opera building or whatever other organization the image of which is tied to the building.
The last image I sold portrays the headquarter of the Food and Agriculture Organization, which is in Rome. That building says "FAO" even when the FAO flag is not visible, and certainly cannot be used by anybody to promote anything without the consent of FAO. But that's not because the building is "copyrighted" (every building on Earth is copyrighted, just like any picture) but because it is linked to the image of the owner. The owner would object to the commercial use of the building as it would imply an endorsement by the organization to the product. That applies to the Moulin Rouge, to Michael Jackson's mansion etc.
The well-known agency Alamy (http://www.alamy.com) has 4822 images of the Eiffel tower at night (just search for Eiffel tower night)
Some organizations (such as the Moulin Rouge or the Eiffel Tower) apply scare tactics to photographic agencies and some agencies are so "timid" to actually withdraw the images without standing their ground as they should. One of these agencies is Alamy, which withdrew all their images of the Moulin Rouge some time ago, without informing the photographers. I had to re-upload my ones. I'm not the only one there are already some hundreds newly available.