SOLVED !
After many attempts at the manual uninstall procedure, which includes the deletion of some MCEBuddy2x registry keys - all of them in subfolders of HKEY_LOCAL_MACHINE\SOFTWARE\ - I searched the ENTIRE registry for MCEBuddy2x keys.
Under the key HKEY_CLASSES_ROOT\Installer\Assemblies\ I found 11 keys common to old version 2.3.10 and new version 2.3.14. After deleting the keys that referred to the old version, I was finally able to install the new version. TA DA !!
After many attempts at the manual uninstall procedure, which includes the deletion of some MCEBuddy2x registry keys - all of them in subfolders of HKEY_LOCAL_MACHINE\SOFTWARE\ - I searched the ENTIRE registry for MCEBuddy2x keys.
Under the key HKEY_CLASSES_ROOT\Installer\Assemblies\ I found 11 keys common to old version 2.3.10 and new version 2.3.14. After deleting the keys that referred to the old version, I was finally able to install the new version. TA DA !!