First of all, thank you for your continued work on FreeFileSync – it's a powerful tool and highly appreciated in the tech community.
I’m a senior system and network engineer, and also a software developer. While installing FreeFileSync on a Windows 11 Pro system, I encountered a specific registry-related error that I believe other users might also face. I’ve analyzed it in detail and would like to share a complete technical breakdown below, in the hopes of helping you diagnose and potentially address it in a future build.
Feel free to incorporate any part of this analysis into your documentation or bug tracking system.
Issue Summary: RegCreateKeyEx failed; code 1021 on Windows 11 Pro
Error message shown during installation:
Windows: Select Action
Error creating registry key:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\Windows Error Reporting\LocalDumps\FreeFileSync_x64.exe
RegCreateKeyEx failed; code 1021.
Cannot create a stable subkey under a volatile parent key.
→ Retry
→ Ignore the error and continue
→ Abort installation
Environment Details
Operating System: Windows 11 Pro (up to date)
Installer: FreeFileSync_x64.exe
Privileges: Launched as Administrator
Technical Root Cause
This error corresponds to:
Code 1021 (0x3FD): ERROR_CHILD_MUST_BE_VOLATILE
It means that the registry key you're trying to write (under LocalDumps) cannot be created as a persistent key because its parent was created with the REG_OPTION_VOLATILE flag—intentionally or unintentionally.
� Reproduction
1. Launch the FreeFileSync installer as Admin on a clean Windows 11 system.
2. Wait for registry writing to reach the LocalDumps section.
3. The error pops up and cannot be bypassed by retrying.
✅ Workarounds & Recommendations
option: Check Volatility
Action: Use RegQueryInfoKey to detect if the parent key is volatile before calling RegCreateKeyEx.
option: Match Key Type
Action: Create the subkey with REG_OPTION_VOLATILE if the parent is also volatile.
option: Optional Installer Switch
Action: Add an option to skip dump registration if it's non-critical.
option: Fix Existing Key
Action: Manually delete and recreate LocalDumps as non-volatile prior to install:
Remove-Item -Path 'HKLM:\Software\Microsoft\Windows\Windows Error Reporting\LocalDumps' -Recurse
New-Item -Path 'HKLM:\Software\Microsoft\Windows\Windows Error Reporting\LocalDumps'
A simple conditional check in your installer logic to detect volatile parent keys would make this bulletproof, even in edge-case environments. Optionally provide a fallback or clearer error message to the end user.
If you'd like help testing a patch or alternative installer approach, I’m happy to collaborate further. Please feel free to reach out.
Kind regards,
