Lewis and Clark has hit another bump in the road — and this time it's entirely changing course.

HBO is all but abandoning the six-part miniseries starring Casey Affleck and Matthias Schoenaerts. "We have decided to redevelop Lewis and Clark with Michelle Ashford writing," HBO said in a statement to The Hollywood Reporter, confirming that it is going back to the drawing board with the high-profile historical drama.

Ashford, who is currently serving as the showrunner on Showtime's Masters of Sex, penned the original script with Ed Norton and John Curran (The Painted Veil). Once her rewrite comes in, the cabler will have to greenlight the project a second time. In the event that the new version does move forward, HBO will then evaluate whether or not previously shot footage is usable (sources say several episodes were filmed) and if roles will be recast.

The project, which had been gestating at the network for years before it got the go-ahead, first suffered a blow in August when it lost its director, Curran, and director of photography, Roby Hardy, over creative differences. Production was shuttered in the wake of the key departures, with filming reportedly set to pick back up in the spring. Now, it’s unclear whether production will ever start up again. Sources say that the series’ props and costumes are being held in storage in Canada, where the first iteration was shot.

Based on Stephen E. Ambrose's book Undaunted Courage, the miniseries hails from executive producers Tom Hanks, Brad Pitt and Norton. It tells the epic journey of the Corps of Discovery and its captains, Meriwether Lewis and William Clark, as they traverse uncharted territory on a mission to deliver President Jefferson's message of sovereignty and search for the fabled all-water route to the Pacific. From HBO, National Geographic Entertainment, Playtone, Plan B and Class 5, Gary Goetzman and Dede Gardner also serve as exec producers.

Affleck, whose Kenneth Lonergan-directed Manchester by the Sea recently premiered at Sundance to rave reviews, had been playing the titular role of Meriwether Lewis, with Schoenaerts as William Clark. It’s unclear if Affleck, Schoenaerts or any of the other cast members will return should the series get a second go. It's worth noting that Affleck is rumored to be fielding multiple pilot offers (though it's unclear if he'll take any of them) and the actress who was set to play Sacagawea, Tanaya Beatty, just signed on to NBC’s Night Shift as a series regular. Affleck's reps declined to comment, while Schoenaerts' camp could not be reached.

For Ashford’s part, she’s currently working for rival pay cabler Showtime on the fourth season of the Michael Sheen-Lizzy Caplan period drama about real-life sex researchers William Masters and Virginia Johnson. Lewis and Clark, for which she also serves as a co-exec producer, marks her third historical miniseries for HBO. She was a writer on the cabler's Emmy-winning John Adams and The Pacific, the latter of which she also served as a co-producer.

The news of Lewis and Clark’s setback comes in the midst of internal struggles at HBO. At the end of January, Michael Ellenberg — who worked on upcoming shows including David Simon’s The Deuce — left his post as the head of drama, with Casey Bloys now overseeing both comedy and drama. On top of the exec shuffle, the network has hit a number of roadblocks on its upcoming series.

In August, David Fincher cut ties with the network, dropping both of his projects, Utopia and Video Synchronicity, and returning to his House of Cards home Netflix to develop a new drama, Mindhunter, with Charlize Theron. In January, HBO’s pricey J.J. Abrams-produced futuristic drama Westworld — which has long been the subject of rumors of a complicated production — shut down to give creators Jonah Nolan and Lisa Joy more time to catch up on their four remaining scripts. A premiere date for the drama has yet to be announced, though insiders say HBO is committed to debuting the Warner Bros. Television series later this year.

And then there’s True Detective. Despite a critically panned second season, HBO programming president Michael Lombardo has been vocal about wanting more of the true crime anthology. "I'd happily be in business with him for a long time," the exec said of the drama’s creator Nic Pizzolatto at the Television Critics Association press tour in July, noting that he’d already opened the door for a third installment. The series’ future remains unclear, however, as it is Pizzolatto’s call.

HBO is currently gearing up for the launch of '70s music drama Vinyl, which THR chief TV critic Tim Goodman called "a thing of real beauty," as well as the return of Lena Dunham’s Girls in February.