If you get an error message, copy and paste the exact command from this page and try again.
Be aware that if you have changed the installation path for Skype then you will need to enter the correct path for the Skype.exe file.
If this solution fails, you can try another option:
Find the Skype executable file (Skype.exe) in: C:\Program Files\Skype\Phone\
Right click on it and select Send to > Desktop (create shortcut)
Locate the shortcut on the desktop, then right-click on it and select Properties
In the Target field, add: /secondary. The Target field should now be "C:\Program Files\Skype\Phone\Skype.exe" /secondary
Click OK. You can now start a new instance of Skype every time you double-click the new shortcut.