To resolve this issue, follow these steps:

• Exit the program if it is open.

Important: The following instructions require you to make changes to the Windows Registry. The Windows Registry is a very sensitive part of windows. If you not do not feel comfortable making changes to the Registry, ask a system administrator to help you. 

How to create a backup of your Registry

• Open the Registry Editor. To do this, press Windows Key+R on your keyboard.
• Type "regedit" in the dialog and press ENTER. The Registry Editor will open.
• Look for the following directory in the Editor: HKEY_LOCAL_MACHINE > SOFTWARE > Wow6432Node > Sony Creative Software > [Program Name] > [Version Number] > License
• Right-click ONLY the folder labeled "License" and select "Delete". 
• After deleting the folder, close the Registry Editor and restart Sound Forge Pro 11. 
• You should now be asked to enter a serial number to register the program.