In version 11.2 you can actually import POSCAR files directly, you would just drop them directly on the Viewer or Builder. The script still works, however, i.e. there are no errors when you just drop it on the "Custom" icon, I trust that is the same for you?
So more likely there is some minor aspect of your POSCAR file that we haven't considered.
Do you have the POTCAR file in the same directory? This is required, otherwise there is no way to determine the element names, since these are not in the POSCAR, except perhaps as optional comments, but we don't want to rely on that in the import filter.
To troubleshoot further we need more details, however. You can email the POSCAR file to me privately if you don't want to share it here. Also, it would help to know if there are any error messages?