hey guys i realize this issue has already been solved, but i was having the same issue as OP and after reading everyones input, i came up with an alternate solution if one does not want to set up the MSAA with enb.Â
So, what i did: Completely turn off AA in the skyrim settings. Open up AMD Catalyst control center(i dont have nvidia but i would assume they have the same thing), go to the gaming section, then 3D application settings. in this window you can tell catalyst to override application settings for AA, and then simply select whatever level and method of AA you desire, click apply. And voila. You will now have as high AA as you want enabled in skyrim, but without the nasty black lines.
Long story short, turn off AA in skyrim settings, open up graphics card control center and tell it to override game application settings with the settings you choose in the control center.
*on a side note, i want to thank everyone who contributed with this thread, i just got a new graphics card yesterday, so naturally i went nutso with mods for skyrim. I noticed this issue and was pissed cuz i thought it was a faulty graphics card, come to find out, just another one of Bethesda's silly little bugs that everyone has come to love oh so much.