After an initial test, I observed the issue as you mentioned by loading your template XLS file via Aspose.Cells APIs. I found NullReferenceException while loading the XLS file into Aspose.Cells’ object model.
We have looked into your source excel file and found it is corrupt when opened in MS-Excel 2013. However, we have fixed this issue CELLSJAVA-41861 now. We will soon provide the fix after performing QA and including other enhancements and fixes.