  We compute the dominant term in the expansion in rho=1-M_W/m_t of the unknown
next-to-next-to-leading order (NNLO) nonresonant contributions to the e+ e- ->
W+ W- b bbar total cross section at energies close to the top-antitop
threshold. Our analytic result disagrees with a previous calculation by other
authors [1]. We show that our determination has the correct infrared structure
needed to cancel the divergences proportional to the top width arising in the
resonant production of the same final state, and we point out to a missing
contribution in the computation of [1] to explain the discrepancy.
