Bloom!
Just got Bloom working with the Neo4j Server using Neo4j 1.2.7, and then some users needed to upgrade their Neo4j Desktop and now find a problem with Neo4j Desktop 1.2.8 - error as in the topic line when Neo4j Bloom loads.
Those who have 1.2.7 installed for a while seem to work ok. Those using Windows variant of the latest Neo4j Desktop Bloom version (1.2.8) can also use Bloom, but those with a MacBook and using 1.2.8 get the incompatibility error.