Registry First Aid can scan the registry for different error categories. Initially, all found registry items are grouped by error category.
See a Screenshot.
And they have different icons when displayed in the list grouped by safety level.
Invalid Paths.
Registry entries containing references to nonexistent files or folders.
Invalid Fonts.
Invalid records of installed fonts.
Auto Run Programs.
Registry keys with auto-start programs. Invalid entries are selected for correction by default. All other entries are listed for your information only.
Obsolete Start Menu Items.
Entries remaining after deleted or moved shortcuts from the Start Menu.
Invalid Help Files.
Invalid records of help files registered in the system.
Invalid Application Paths.
Invalid records of applications registered in the system.
Invalid Shared DLLs.
Entries remaining after deleted or moved common DLL files, removed applications.
Invalid Known DLLs.
Invalid DLL aliases remaining after moved/deleted .dll files.
Unused Software Entries.
Empty registry keys remaining after removed programs. Entries that do not contain any values. Unused keys may have unlimited number of sub-keys but all of them must be without values.
Invalid File Associations.
File types and extensions incorrectly registered in the system.
Invalid COM/ActiveX references.
ActiveX/COM incorrect registrations or records remained after removed components.
Invalid Uninstall records.
Incorrect program installation records.
Invalid TypeLib references.
Incorrect records under TypeLib registry key.
Invalid Firewall rules.
Invalid or obsolete entries under the Firewall Rules registry key.