Outlook once more: Outlook does not allow to add new signatures

This problem appeared on a brand new installation of Outlook 2016 where the user was unable to add a new signature. After some searching and trying several other solutions this one fixed the problem, one more time a registry entry has to edited/added:

Find the following key in the registry, for 32-bit installation:
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{0006F03A-0000-0000-C000-000000000046}\LocalServer32

For 64-bit installation it is:
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Wow6432Node\CLSID\{0006F03A-0000-0000-C000-000000000046}\LocalServer32

In the right pane of the LocalServer32 key, for both registry strings (REG_SZ) named (Default) and LocalServer32 set their value:

For 32-bit Office installation of Outlook 2013 on 32-bit Windows and for 64-bit Office installation on 64-bit Windows:
C:\Program Files\Microsoft Office 15\root\Office 15\Outlook.exe

For 32-bit Office installed on 64-bit Windows:
C:\Program Files(x86)\Microsoft Office 15\root\Office 15\Outlook.exe

For Outlook 2016 replace number 15 above with 16 !

Good luck !

See also:
http://www.thewindowsclub.com/unable-to-add-signature-in-outlook


UPDATE 2019-09:

There is another known reason which can block the signature function on clients with Windows 10, the App "Microsoft Office Desktop Apps" can cause this problem. Uninstalling the App via the Windows Settings / Apps & Features can fix it - see also https://answers.microsoft.com/de-de/msoffice/forum/msoffice_outlook-mso_win10-mso_2016/outlook-2016-signaturen-briefpapier-%C3%B6ffnet/3b1439fc-2606-4306-b2d3-57a5ce440163