Complementary studies are reported from the DIII-D and JET tokamaks, exploring the role of error fields in the triggering of 2/1 tearing modes at high Beta. In all cases a strong lowering of BetaN thresholds (~20 to 60%) is observed even when modest levels of error field (~2-4G) are applied. On JET, the effect appears to be a manifestation of increasing error field sensitivity at high BetaN, leading to strong coupling and directly inducing locked modes. Conversely on DIII-D rotating modes are observed indicating error fields may be changing the underlying metastability of the NTM. The role of sideband harmonics is also important in determining the degree and location of magnetic braking.