That loading error is usually down to a mismatch between the header and the actual data in your file. If Slicer can’t find the specific volume dimensions or spacing it expects, it’ll just hang or throw a generic error. A quick thing to try is using the “Add Data” dialog but checking the “Show Options” box. Sometimes manually setting the file type to “Volume” instead of letting it auto-detect fixes the hang. If it’s a DICOM issue, you might want to try importing it through the DICOM Browser module first rather than just dragging and dropping the file.
If you’re still stuck, check if there are any special characters or spaces in the file path - Slicer can be a bit picky about those depending on the OS.