This can happen for a variety of reasons, including...
Not enough space on your device's hard drive (this primarily only applies to desktop and laptop computers, but there is also some indication that this may be happening with certain mobile devices).
Your operating system needs to be updated.
You could be using an old web browser and need to either update it or use a different web browser. We highly recommend using Google Chrome if possible.
Please click here for more information on some steps you can take and why this may be happening.