I am afraid, it is hard to tell what could have gone wrong by just inspecting the stack trace. It would be of great help in isolating the problem cause if you can share an executable piece of code along with the problematic sample. Before you move forward to provide us the above requested, please give a try to the latest version of the Aspose.Cells for Java 17.02.4 (attached) to see if you can still replicate the issue,