  In the calculation of the anomalous magnetic moment of $W^\pm$ bosons, we
discuss vector anomalies occuring in the fermion loop that spoil the predictive
power of the theory. While the previous analyses were limited to using
essentially the manifestly covariant dimensional regularization method, we
extend the analysis using both the manifestly covariant formulation and the
light-front hamiltonian formulation with several different regularization
methods. In the light-front dynamics (LFD), we find that the zero-mode
contribution to the helicity zero-to-zero amplitude for the $W^\pm$ gauge
bosons is crucial for the correct calculations. Further, we confirm that the
anomaly-free condition found in the analysis of the axial anomaly can also get
rid of the vector anomaly in LFD as well as in the manifestly covariant
calculations. Our findings in this work may provide a bottom-up fitness test
not only to the LFD calculations but also to the theory itself, whether it is
any extension of the Standard Model or an effective field theoretic model for
composite systems.
