Even seasoned technicians encounter serial number issues. Below is a troubleshooting table for the most frequent error codes and messages related to the FANUC Ladder III serial number.
| Error Message | Probable Cause | Solution |
|---------------|----------------|----------|
| "Invalid serial number. Installation aborted." | You entered the dongle serial instead of the software install serial. | Confirm the correct number from the CD sleeve. |
| "License check failed. Dongle not found." | The USB dongle is not inserted, or drivers failed to load. | Re-insert dongle. Try a different USB port. Reinstall dongle drivers from C:\FANUC\Driver. |
| "Serial number mismatch." | The dongle’s serial does not match the one entered in the software authorization. | Run FL-III, go to Help > License Manager, and re-enter the correct dongle serial. |
| "Demo mode – 30 days remaining." | No dongle serial entered, or dongle is for a different FANUC product (e.g., Ladder II). | Purchase a valid FL-III dongle or contact FANUC for upgrade. |
| "This serial number has been revoked." | The dongle was reported lost/stolen, or a previous license transfer was incomplete. | Contact your regional FANUC office with proof of purchase. | fanuc ladder iii serial number
If LADDER-III is already installed on a PC: Even seasoned technicians encounter serial number issues
If the dongle is also lost, you may need to purchase a new FL-III license. As of 2025, a new single-user license costs approximately $1,200–$1,800 USD depending on the version (Standard vs. Professional). If LADDER-III is already installed on a PC: