In following the directions for https://developers.redhat.com/products/fuse/hello-world/#fndtn-karaf-runtime, got into a situation where we were getting a ClassNotFoundException on org.apache.log4j.Level during the JUnit tests. The 1.2.17.redhat-1/log4j-1.2.17.redhat-1.jar JAR existed within ~/.m2/repository/log4j/log4j, and when I jar tvf'ed it, I could see the org.apache.log4j.Level.class inside of it. However, even when running mvn clean install from the Windows command line (completely outside of maven), the ClassNotFoundException on org.apache.log4j.Level reproduced.
Solved the issue by closing Eclipse, deleting the .m2 directory completely, opening Eclipse, and doing a Maven Update on the project. Was then able to build the project. Seemed like it may have been some sort of permissions error because it did not seem like the JAR itself was corrupted.