At the end of the 'setup', after pressing 'Done', the process stops at the 21st participant and the Error is: 
No suprathreshold voxels in ROI file --------- after erosion (original file contained 164 suprathreshold voxels).

What is the meaning of this error and what can I do in order to solve it?

I checked the structural file and the ROI fles and they both seem fine.

Thank you !