| Problem | Likely Cause | Solution | | :--- | :--- | :--- | | “Product Key Invalid” | You typed 001M1 for a different year or product | Verify you are installing AutoCAD 2021, not 2020 (Key: 001L1) or 2022 (Key: 001N1) | | “Serial Number Blocked” | You bought a blacklisted key (e.g., from eBay or a student reseller) | Contact Autodesk support. You need a refund from the seller. | | Installation stops at 0% | Antivirus blocking the installer or corrupted download | Temporarily disable antivirus. Re-download from your Autodesk account. | | “License Checkout Failed” | Network license server offline | Contact your IT department. For single-user, check your internet connection. |
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