I guess it’s memory problem. Your computer froze because it’s swapping due to limited memory. We updated ANTs parameters (hopefully improve the precision) in the latest release. ANTs SyN itself is very memory demanding, especially if you use ANTs SyN + Subcortical Refine. So better to run it on a machine with large RAM. ANTs SyN + Subcortical Refine can take 20-30GB memory. ANTs SyN may also take 10+GB memory.
In the development version of lead, we preset some ANTs parameter sets with some other settings in the setting window, from which you can choose the SyN Quick one if you want to do a quick test with ANTs and your system has limited memory.