That is only a warning to let you know that you are dealing with an oblique dataset. As the warning indicates, there can be problems mixing data of differing obliquity, and these may not display correctly with differently oblique datasets in the AFNI GUI. If you already know that, then you can safely ignore that warning. There is an environment variable to turn that off, AFNI_NO_OBLIQUE_WARNING, that you can set to YES in your .afnirc file.

The bigger question is what these datasets are and what you are trying to do with them. The mask seems to be in a standard space (+tlrc view of the dataset), and your dataset is oblique, unlikely for a dataset in a standard template space. If the two are in different spaces, then resampling isn't what you want to do; you need to apply spatial transformations to either the mask or to the original dataset to bring it into the space of the other. Maybe, you've picked the wrong datasets for this operation?