If you cannot find a safe v3.51.01 file, consider leaving your TV on its current firmware. LG never released a critical security or performance patch for this model after ~2010.
Re-verify that the folder name is exactly LG_DTV in uppercase. If it still fails, try a different, older USB stick. Drives formatted on Mac computers sometimes leave hidden partitions that confuse old LG TVs; format the drive on a Windows machine if possible. lcd tv lg firmware 32lg3000 v35101 updated install
Check the "Software Version" to ensure it displays v3.51.01. If you cannot find a safe v3
Once the update is complete, the TV will turn off and on again. Once it starts normally, go to the menu to verify that the software version has updated to v3.51.01. Troubleshooting: Firmware Update Fails If it still fails, try a different, older USB stick
If you still want to attempt 3.51.01, ensure you have a backup of your current firmware (unlikely possible on this model) and accept the risk of failed downgrade.
Resolves issues where audio drops out unexpectedly when switching between digital Freeview channels or external HDMI sources.