I have my build dir to a RAM drive to speed up the building process. It seems that the editor does not synchronize its
content with the build folders properly: it shows errors as if it couldn't find the classes that belong to the project.
This happens mainly with the test classes. 
I tried to solved the problem by running the clean task followed but the comp-tests tasks, but the editor still shows
that  it can't find the classes when they're in fact there (sometimes this also happens in the Projects windows, but
running those two tasks seemed to solve the problem). 
If I close the window that shows the class marked with errors and re-open it, then everything goes back to normal.
Let me know if I can help you in any way to solve the problem.
Thanks,

Marcelo