You may have moved the application to the SD card to save space on your phone’s internal drive. The widget functions only if the application is saved on the internal drive. This is a current limitation of the Android OS.
Android doesn't allow you to install an application to the SD card and still have the widget, so when the app is moved to the SD, the widget is removed.
To restore the widget, you must delete the application then reinstall to your phone's main memory and you can then restore the widget.