Upgrade to 5.0.0 resulted in IOException message

Here is what I get when running using the 5.0.0 APIs:
java.io.IOException: Your InputStream was neither an OLE2 stream, nor an OOXML stream or you haven't provide the poi-ooxml*.jar in the classpath/modulepath - FileMagic: OLE2, having providers: [org.apache.poi.xssf.usermodel.XSSFWorkbookFactory@40086342]  
at org.apache.poi.ss.usermodel.WorkbookFactory.wp(WorkbookFactory.java:300)  
at org.apache.poi.ss.usermodel.WorkbookFactory.create(WorkbookFactory.java:210)  
at org.apache.poi.ss.usermodel.WorkbookFactory.create(WorkbookFactory.java:163)  

Note: It works when running in my IDE; however, when it runs from a (mega) jar (built by ant), we get the exception above.

I am wondering if it has something to do how the jar is being built; however, it did/does work with the 4.1.2 jars.

Thoughts on where to look?

Thank you!