How to make alarm or show popup message

I want to show user by alret or popup that this task due date is soon in his tasks list.

Which event/activity I can use for this?
I tried timer but it didnt do anything

Thank you

Error message when attempting to open the program


When attempting to launch the program, this is the message I receive. I am a novice so no clue as to what this means.

The JVM shared library "/Applications/BonitaBPMCommunity-6.5.1/jre/Contents/Home/jre/bin/../lib/server/libjvm.dylib" does not contain the JNI_CreateJavaVM symbol.

I am running on a Mac, OSX 10.10.3 and Java version 8 - 45 (build 1.8.0_45-b14)

Thanks for your help in sorting this out...