I am starting to configure my development environment and I am using Spring Tool Suite 2.8.1 along with m2E 1.01.
As far as I can tell, since this is a Maven Project
none of the solutions above helped my problem. I've resolved it by deleting all files in {projectworkspace}/.metadata folder AND in {location}/.m2 folder and let eclipse download every single thing again. Hope this helps someone, cheers!