FULL PRODUCT VERSION :
java version "1.8.0_101"
Java(TM) SE Runtime Environment (build 1.8.0_101-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.101-b13, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Windows 10 Pro

EXTRA RELEVANT SYSTEM CONFIGURATION :
Using Netbeans 8.1

A DESCRIPTION OF THE PROBLEM :
On compiling project this appears:

An exception has occurred in the compiler (1.8.0_101). Please file a bug against the Java compiler via the Java bug reporting page (http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com) for duplicates. Include your program and the following diagnostic in your report. Thank you.
java.lang.IllegalStateException: endPosTable already set
	at com.sun.tools.javac.util.DiagnosticSource.setEndPosTable(DiagnosticSource.java:136)
	at com.sun.tools.javac.util.Log.setEndPosTable(Log.java:350)
	at com.sun.tools.javac.main.JavaCompiler.parse(JavaCompiler.java:667)
	at com.sun.tools.javac.main.JavaCompiler.parseFiles(JavaCompiler.java:950)
	at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.<init>(JavacProcessingEnvironment.java:892)
	at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.next(JavacProcessingEnvironment.java:921)
	at com.sun.tools.javac.processing.JavacProcessingEnvironment.doProcessing(JavacProcessingEnvironment.java:1187)
	at com.sun.tools.javac.main.JavaCompiler.processAnnotations(JavaCompiler.java:1170)
	at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:856)
	at com.sun.tools.javac.main.Main.compile(Main.java:523)
	at com.sun.tools.javac.main.Main.compile(Main.java:381)
	at com.sun.tools.javac.main.Main.compile(Main.java:370)
	at com.sun.tools.javac.main.Main.compile(Main.java:361)
	at com.sun.tools.javac.Main.compile(Main.java:56)
	at com.sun.tools.javac.Main.main(Main.java:42)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
In netbeans, load project, clean/build/edit/run without problems for some days
Until eventually clean and build fails.
Run clean - succeeds.
Run build, fails and produces the above message.
Clean again - succeeds.
Run build again - succeeds.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Clean and build succeeds every time
ACTUAL -
build occasionally fails 

ERROR MESSAGES/STACK TRACES THAT OCCUR :
An exception has occurred in the compiler (1.8.0_101). Please file a bug against the Java compiler via the Java bug reporting page (http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com) for duplicates. Include your program and the following diagnostic in your report. Thank you.
java.lang.IllegalStateException: endPosTable already set
	at com.sun.tools.javac.util.DiagnosticSource.setEndPosTable(DiagnosticSource.java:136)
	at com.sun.tools.javac.util.Log.setEndPosTable(Log.java:350)
	at com.sun.tools.javac.main.JavaCompiler.parse(JavaCompiler.java:667)
	at com.sun.tools.javac.main.JavaCompiler.parseFiles(JavaCompiler.java:950)
	at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.<init>(JavacProcessingEnvironment.java:892)
	at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.next(JavacProcessingEnvironment.java:921)
	at com.sun.tools.javac.processing.JavacProcessingEnvironment.doProcessing(JavacProcessingEnvironment.java:1187)
	at com.sun.tools.javac.main.JavaCompiler.processAnnotations(JavaCompiler.java:1170)
	at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:856)
	at com.sun.tools.javac.main.Main.compile(Main.java:523)
	at com.sun.tools.javac.main.Main.compile(Main.java:381)
	at com.sun.tools.javac.main.Main.compile(Main.java:370)
	at com.sun.tools.javac.main.Main.compile(Main.java:361)
	at com.sun.tools.javac.Main.compile(Main.java:56)
	at com.sun.tools.javac.Main.main(Main.java:42)

REPRODUCIBILITY :
This bug can be reproduced rarely.

---------- BEGIN SOURCE ----------
The code is not changed, yet the build problem resolves with persistent clean and build requests.  I suggest this is not code related.
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Try again a few times.  Restart netbeans if needed.  Reboot machine if needed.