This has been an issue with some versions of Microsoft Office, when uninstalling Click to Convert using the Add/Remove Programs option in the Windows' Control Panel.  This most frequently happens with Office 2007 but may happen with other versions.

To correct this issue:

(NOTE: This procedure involves editing the registry for MS Windows.)

Windows 64-bit Users

1. Close all applications (especially MS Office applications such as Word, Excel, PowerPoint, etc.).
2. Go to the Start menu and choose Run or if Run doesn't exist in the menu, click in the search box.
3. Type regedit and click ok to start the regedit application.
4. On the left panel (side) of the Registry Editor, navigate down to the following folder/location:
   HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/Office/12.0/PowerPoint/AddIns
5. Remove the folder named ClickToConvert (highlight and select Delete from the EDIT options).
6. Close the Registry Editor.

(NOTE: If you don't find the ClickToConvert add-in entry in the above location, search in the following locations also:

HKEY_CURRENT_USER/SOFTWARE/Microsoft/Office/12.0/PowerPoint/AddIns

HKEY_CURRENT_USER/SOFTWARE/Microsoft/Office/11.0/PowerPoint/AddIns

HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/Office/11.0/PowerPoint/AddIn

Windows 64-bit Users

The registry entries above are a little different if you are using Windows XP, Vista, 7 or later and you have a 64-bit version of Windows installed. 

In addition to the above locations, you should look in the following Registry locations (note the addition of the Wow6432Node folder in these locations):-

HKEY_CURRENT_USER/SOFTWARE/Wow6432Node/Microsoft/Office/12.0/PowerPoint/AddIns

HKEY_CURRENT_USER/SOFTWARE/Wow6432Node/Microsoft/Office/11.0/PowerPoint/AddIns

HKEY_LOCAL_MACHINE/SOFTWARE/Wow6432Node/Microsoft/Office/11.0/PowerPoint/AddIn

HKEY_LOCAL_MACHINE/SOFTWARE/Wow6432Node/Microsoft/Office/12.0/PowerPoint/AddIns

Failing that, you can simply search your entire registry for any occurances of ClickToConvert and delete them.