The monster Nerozar the Defeated has a listed speed of "20 ft., walk 0 ft.". This give it two walking speeds, which shouldn't be the case. Nerozar comes from chapter 3 of WDotMM and is based on the beholder zombie which has a speed of "0 ft., fly 20 ft. (hover)", which is probably what Nerozar's speed should be replaced with.

This error was pointed out on Nerozar's stat block page by a comment. I've come across this a few times where comments on a monster page point out a problem that never gets reported. It would be nice if there was an easy way to report these kinds of errors directly from each monster's page.

I can confirm this. Nerozar the Defeated isn't given a specific statblock in the adventure module, only described as a beholder zombie with a modification to one of its Eye Rays. The speed is definitely a mistake on DDB's end and not due to a typo in the module.