Version 5.02 just release with 22 changes... BIG upgrade! 
We are still lacking the feature to "Merge Duplicate BookIDs" that was available in past versions. It got too complex to get in 5.03, but is scheduled to be added in 5.04.
To avoid needing to renumber duplicate BookIDs, do as Lonman suggests to always press the "Next" (BookID Root) to get an unassigned BookID Root number. But, be careful to NOT be importing on BOTH computers. That could cause duplicate BookIDs.