Error using wmb2bediutiladdICEnvelopeEDIFACT

I am try to create an EDIFACT envelope using the
wm.b2b.edi.util:addICEnvelopeEDIFACT flow step from the
WmEDI package in SAPBC 4.6. I have my EDIFACT data as a
string in the documents stringList (UNH to UNT)

When I call the addICEnvelopeEDIFACT flow step I get the
following error
java.lang.reflect.InvocationTargetException:com/wm/app/tn/tspace/Reservation

It appears to be failing in the convertToString inside the
addICEnvelopeEDIFACT.
Has anyone seen this or know how to fix it?

Cheers,
Simon

you can check if the
wm.b2b.edi.EDIFFSchema:ICS4UNEDIFACTNEW exists