At first i thought it may be something with my computer but after trying in a whole different setup,everytime i try to open the WSYIWYG it opens the window and then it closes automatically. I went back to 8U66 (my latest JDK) and it opens without problems.
I am having the same problem with JDKU8U102 on windows 10. The WYSIWYG designer connects, displays the WYSIWYG form very quickly and then closes. The Abstract designer works fine. However it works fine with b4j 4.5 beta.