I've recently got a fresh new licensed IntelliJ IDEA 12 and have been so glad about it until I've suddenly stumbled upon a strange issue. The Java project that was being developed successfully in previous versions of IDEA crashed during building this time. Shortly, the solution was hidden under IDEA Settings Compiler.Excludes where the JAXB generated sources directory was excluded due to some unknown reason. Below are the details and the screenshots. Symptoms of issue Here are the symptoms of the issue. Whenever the sources directory is excluded from compiling, it's marked with cross signs. See generated directory below: This issue results in numerous "cannot find symbol" errors during compilation: Settings Compiler.Excludes Here is the screenshot with the solution for this issue. You just need to delete the item with excluded sources and they will again magically appear in the classpath. Update - the root cause found After a while I real...