I'd like to elaborate a little on the reason why a Nestor isn't accepted.
If you compare that to the Nightmare posted on our Fittings website you'll find the following:
First and foremost, the Nestor gets most of its DPS from Drones, which means its damage it delayed. It also makes it a really poor Sniper which means it would almost certainly have to run with the DPS squad.
The Nightmare can also fit 3 Tracking Computers by default, plus two Utility Highs. This means that it applies the damage it deals much better than the Nestor.
Also while that Nestor fit is cheaper than a Nightmare it's not significantly cheaper, and it performs worse for that price.
On the whole we'd really rather not encourage people to bring expensive and significantly non-optimal ships like that. A Hyperion requires the same ship skill and not too much additional gun training to fly and overall adds more to the fleet for less ISK on grid than a Nestor does.
It sucks when a ship you like doesn't work for something you want to use it for, but we can't have everything.
Hope to see you in fleet soon! o7