This may not be a JBoss Tools problem at all, may be an m2Eclipse problem, but I figured I would post here since I did see JBoss Tools errors several times.
Basically, when I add the 1.9.1 version of Amazon's aws java api as a dependency in my project, the environment goes totally nuts. It rambles along for a long time trying to build then fails saying it was unable to read the Artifact Descriptor of the guava project (a transitive dependency of aws). When I comment out the dependency in the pom, it builds fine. (Version info in tags.)