Q: cannot remove lock down file

Can you explain "lock down file" more clearly?  If iTunes doe not recognize you iPhone, then this may help:

If iTunes doesn't recognize your iPhone, iPad, or iPod - Apple Support

If that is not the issue, then I think you need to explain & rephrase your problem again.

If your iOS device isn't showing in iTunes try the following:

1. Open Control Panel > Device Manager
2. Plug in your device
3. Locate Universal Serial Bus Controllers > Apple Mobile Device USB Driver.
   It is also possible the device may show under Imaging Devices, Portable Devices or Other Devices or as an MTB USB Device.
4. Right-click and select Update Driver Software...
5. Click Browse my computer for driver software
6. Browse to C:\Program Files\Common Files\Apple\Mobile Device Support\Drivers or
                   C:\Program Files (x86)\Common Files\Apple\Mobile Device Support\Drivers
7. Click Let me pick from a list of device drivers on my computer
8. Click Apple Mobile Device USB Driver
9. Click Next, then Close and exit Device Manager

For step 3 above, open the device manager. Expand any of these sections that are listed.

• Universal Serial Bus Controllers
• Imaging Devices
• Portable Devices
• Other Devices

Connect the device. You should hear the telltale sound of Windows device connection and one section should gain a new entry. That should be your device. It may not be labelled correctly at this stage. If you don't hear a noise suspect a damaged cable.

Or try If iTunes doesn't recognize your iPhone, iPad, or iPod - Apple Support which is Apple's version of the advice above.

Failing that try a full tear down and rebuild of iTunes as set out in Troubleshooting issues with iTunes for Windows updates. 64-bit users could also try the alternate Download iTunes for Windows (64-bit - for older video cards) build which is sometimes a useful workaround.

Or lastly try rolling back to the last build of iTunes that worked for you. See iTunes installers for download links. If you're rolling back from 12.4.0.119 to 12.3.3.17 or 12.3.2.35, for example, then you'll also need to roll back the library database using the method described in Empty/corrupt iTunes library after upgrade/crash. The tip includes suggestions for reintroducing any recent purchases so at worst you lose a few playcounts and/or a recently created playlist.

tt2