In Eclipse, "Update Maven Dependencies" is disabled and greyed-out, why?

I'm using Eclipse STS 2.7.1 and created a new Spring Template/MVC project. I deleted the pom file and replaced it with one from another project that has all the dependencies I need. But when I attempt to update the dependencies, the menu option 开发者_如何学编程is disabled...why?

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Instead of using the Spring Tools maven option, select Maven->Update Dependencies. That should do the trick!