NetBeans "the type of ... is erroneous"

If your Java project builds successfully but NetBeans 8.2 shows red marks in code with the message "the type of ... is erronous", close NetBeans, clear all files inside 8.2 cache folder. On Windows the folder is located in %LOCALAPPDATA%/NetBeans/Cache/8.2

If this does not get rid of red marks, close NetBeans, open project.properties file, Delete any extra "}" at the end of javac.classpath section, e.g. it the final line in that section should not be ${reference.mylib}} but ${reference.mylib}. This usually happens when you manually edit the file.