This post won’t be of direct help but I would suggest that if at all possible to not use Excel as a data format.
Having worked with Excel files before using POI as the tool within IS many moons ago – it worked okay (in Integration Server, not wM.io). The end result was sufficient at the time for what was needed but left me with this rule-of-thumb that I follow to this day – never process Excel files in automated integration scenarios. 
Far too fragile because people manually edit them. “Why did it fail? All I did was insert a column.”
A guess is that there is a library missing on the classpath or potentially a class conflict used by different libraries.