This issue occurs because the punkt resource download was incomplete or corrupted. The punkt tokenizer relies on several underlying files, including punkt_tab. When these files are missing, you encounter a LookupError. While downloading punkt should include all necessary files, explicitly downloading punkt_tab resolved your issue by filling in the missing dependency. To fix this, ensure a complete download of punkt using nltk.download('punkt'). If problems persist, clear existing downloads and re-download punkt. This ensures all required files are available for the tokenizer to function correctly. For me explicity installing punkt_tab resolved the issue for me.