No response when click to switch between different tab in Settings

I have no idea what happened to this great plugin in this particular site: I entered the Settings, there are tabs like: General, Google Calendar, Working Hours, Exceptions, Services, Service Providers, Add-ons, Logs
When I click on any tab, it doesn't take me to the tab, just stay where it is (the General tab).
The behavior is noticed in FF, Chrome and IE.

However, this plugin works just fine in my another site.

Although I don't think other installed plugins might have any impact to it, I did try to un-install other plugins and the result is just the same.

It would be greatly appreciated if anyone can help me to fix it.

Thanks.