This behavior is observed if the XML registration is missing in the system. To fix the problem, use the following steps:
Close Windows Sidebar. To do so, right-click on the Sidebar icon in the Notification area and click Exit
Open an elevated Command Prompt window. To do so, click Start, click All Programs, click Accessories, right-click Command Prompt, and then click Run as administrator.
In the Command Prompt window, type the following and press ENTER:
Similarly, run these commands:
If the registration was successful, you'll see the message DllRegisterServer in <filename> succeeded for each command executed. Open Windows Sidebar (sidebar.exe) and check if the problem is resolved.