Author Karen Traviss announced a while back that she is no longer writing her long-awaited Boba Fett novel. The author explained that contract issues were getting in the way of her story line, and it seems like what she was planning for Boba Fett, and what Lucas was planning on his new TV series, conflicted.
Yes, the Boba Fett novel was canceled by the publisher because of potential canon clashes with the upcoming TV series, as you have already heard from other sources. No, I really don't have a clue what those clashes might be. Sorry.
We can only assume that Traviss was planning to base her portrayal of Boba Fett on the canon already established in the six movies — and the TV series is planning to make some major change, or addition, to that canon. Still, this means more Boba on the screen, which is always a good thing.
So where is this new series set? According to Wookiepedia and The Celebrity Cafe, it takes place in the "dark times" between the last prequel and A New Hope. And if you remember, that's when most of the Jedi and anti-emperor politicians were hunted down and killed. It's being toted as a gritty and dark series, which will star many minor characters as we now know Boba Fett, but also C-3PO, and Emperor Palpatine (nothing has been officially confirmed yet).
As far as past Star Wars characters like Han, Luke and Leia, Mark Hamill says he doesn't think there would be a role for him as in this time period Luke would be even younger than he was in A New Hope. But the actor did praise the decision to return to focusing on the story, instead of the sizzle of CG FX and tedious lightsaber fights.
In an interview with Total Film Magazine Lucas explained that it would be more like the original than the prequels, "
It's [a] lot more talky. It's more of what I would call a soap opera with a bunch of personal dramas in it. It's not really based on action-adventure films from the '30s - it's actually more based on film noir movies from the '40s!"