Making mistakes while manipulating registry could affect your system adversely. So be careful while editing registry entries, also its better to create a System Restore point before proceeding.
1. Press Windows Key + R combination, type put regedit in Run dialog box and hit Enter to open the Registry Editor.
2. Navigate here:
For 32-bit installation:
For 64-bit installation
3. In the right pane of LocalServer32 key, for both the (Default) and LocalServer32 named registry strings, click them one by one set their Value data to:
For 32-bit Office installation 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
Once you’re done with this, close Registry Editor and reboot the machine, your problem should by fixed.