Rebecca Bellovin writes:

Here's one I didn't see on the list on mathoverflow: In exercise 2, part 10, equation (**) (page 353, line 4) should be

    $$\prs{\lambda}{b}=\prod_{v\in S}(b,\lambda)_{v}$$

not

    $$\prs{\lambda}{b}=\prod_{v\in S}(\lambda,b)_{v}$$

(\prs = power residue symbol). The right-hand side should be the reciprocal of what it is in the book.

I recall also having trouble getting the signs in part 14 of that exercise (on cubic reciprocity) to work out, perhaps because of the mess of algebra, perhaps because some of the computations depend on part 10. I'm suspicious of equation (**); I'll try to check it again.