I think the wording here could be improved.
1. No need for 'There is currently ...' as it implies udunits will provide support at some point in the future.
2. There is no real need to mention udunits. That's an implementation detail.
3. The loss of the name is not related to the problem with the units is it?

How about: "Unable to represent the exponential of a cube's units. The units of the resultant cube will be unknown."