For advanced users who are trying to tix weird problems
You really need to know what you are doing when you are dealing at this level.
It turns out that it is safe to delete the build and devel subdirectories in ROS.
Sometimes this helps:
First: lean your build by running "catkin_make clean" in the root of your workspace.
Second: remake your project with "catkin_make"
Third: re-source the devel/setup.bash in your workspace.