That is so dumb. You might have to scrape off what you can, and then sand the deck. If you try to sand it first, it will just foul up the sandpaper.
There might be a solvent...you should contact anchorseal.
If it's an Ipe deck, the wood will be ok.

steve

amazing - hoping it's a bad joke.

Wow, that's the dummest thing I've heard in awhile. Not much hope for that decking. Imo your best bet, or I should say your contractors best bet is to unscrew the boards & flip them over cause that side is history. Dummy should have read up on it's use before using it for a finish.

Forget sanding, that ain't gonna work, maybe a planer.

I'm a woman and even I would not have done this! Anchorseal is for the ends of the boards to keep them from checking/etc. I had a tigerwood deck put down about 18 months ago, the distributor recommended Penofin Penetrating Oil Finish. 90% UV protection, Brazilian Rosewood Oil. I did it initially and should have reapplied it again, but with the business of trying to work and other things that didn't happen. So it has aged a silver color. Not bad but I'm going to pressure wash it and reseal it. Good luck with yours. I think you are screwed! By the way, they sold me a couple of quarts of a wax (probably similar to Anchorseal) to put on all of the fresh cut ends. When the wood was delivered all the ends were already coated. I just needed to reapply for the new cuts. Everything worked out fine.