Obsolete Software Key (Bitdefender) comes up and will not be removed from a Registry issue.
Data: Bitdefender
Registry Key: HKLM\Software\Bitdefender
Why??
Firstly you should not run the registry cleaner on a regualr basis, especially with Windows 10.
It can cause problems or even break your machine if used indiscriminately.
It's a specialist tool to be used sparingly in certain situations and not used as a regular cleaning tool.
(It is going to be moved to the advanced tools section of CCleaner for that very reason).
Do you have Bitdefender? Is it Running?
It may be a False Positive by the Registry Cleaner and either Bitdefender is protecting it from removal (AVs do that for their own files and reg entries) or CC may be removing it and Bitdefender recreating it.
If you have previously uninstalled Bitdefender then how did you uninstall it?
As said above most AVs will protect their own files and settings, to prevent malware removing them; this means that you should use their own uninstallation programmes to remove everything.
Windows or other uninstallers may not be able to remove all of those protected files/settings.
Bitdefender has it's own uninstallation tools: <a href="https://www.bitdefender.com/consumer/support/answer/2791/" rel="external nofollow">https://www.bitdefender.com/consumer/support/answer/2791/</a>
The tools themselves can be found here: <a href="https://www.bitdefender.com/uninstall/" rel="external nofollow">https://www.bitdefender.com/uninstall/</a>
(You may need to reinstall Bitdefender and then run the uninstallation tool to remove it completely).