title: Android eclipse - Exclamation mark next to project name
body: <p>I changed the dependent projects of one of my project and moved one of my files there as an experiment.
  I now moved it back but the project won't run.
  It tells me I have an error even though I can't see one and "Clean project" doesn't help.
  However, the project has an exclamation mark next to it. What does that mean?</p>