I have uninstalled, reinstalled different versions of 3D Slicer and the same error message keeps appearing. I am at a loss of what to do to get it working again. Any help would be very appreciated.
TotalSegmentator can only segment CT images. Please retry the segmentation on a CT image as described in the tutorial.
Error 120 is often caused by incorrect PyTorch installation. Reinstall the latest Slicer Stable Release (currently 5.6.1) in a new folder and install PyTorch manually as described here.
Please see the following post regarding a required workaround even when using CT images. Note this may change as the various dependencies of the TotalSegmentator python package change.