the gemara states that bitul rehus can never work if people participating in the eruv are mevatel reshus to two people who forgot to participate in the eruv....but why cant the people in the eruv do bitul reshus to one of the two who had forgotten to be in the eruv and then the other who had forgotten will also be mevatel his reshus to that person (this question originally asked by lenny greenberg of forest hills)
bezalel ostrow, new york city
The Meiri explains that if the two who did make an Eruv are Mevatel their reshus to one of the two people who did not, this first Bitul Reshus is invalid. This is because it does not allow this first person to use the yard, as the second person who did not make an Eruv still forbids him from using the yard. Therefore, the first person cannot be Mevatel Reshus to the second person as the first person's Bitul was never valid.
All the best,
Yaakov Montrose