Dear Kangjoo,

First of all, happy new year ! For the cases where coregistration between fMRI and T1 fail, you can try to tweak the parameters of nu_correct for the T1 (for example 50 instead of 75). It does not necessarily improve the T1 nu-correct per say, but it just perturbates the fMRI-T1 coregistration process a bit, and it ends up converging. You should be able to correct problematic cases in one or two iterations.

Best,