Hi Simon,

A wild guess: can you duplicate the mask file, one named mask_metaROI.nii.gz and the other mask_metaROI_2mm.nii.gz?

Also, keep in mind that if you didn't get a indexes file for that mask, you won't be able to run the fwe correction. Custom indexes file are usually generated by us (the sdm team). Did you contact any of the members of the team in order to generate the indexes file?

Hope this helps,

best,

Anton