Sometimes for reasons unknown Eclipse start to give errors for project which simply do not make sense. The symptoms are:
1. Errors that say something like:
java.lang.RuntimeException unable to get class information for @throws tag for [an exception]
2. Package declarations are maked red.
The cause of this is quite simple: Checkstyle plugin. When it tries to run it does not find some classes and given the above error message.
The solution is quite simple:
1. open the project properties (select project and hit alt+enter or select properties from context menu) and go to "Checkstyle"
2. disable checkstyle (the project will rebuild)
3. enable checkstyle (the project will rebuild)
And all your errors will go away.
If you have more than one project in your workspace you will need to perform the above procedure for every single one of then (sorry...).