Attempting to serialize an Assocation in GemStone 3.7.5 results in a DNU. STONWriter>>writeAssocation: is missing. This problem does not exist in earlier version of GemStone.
In GemStone 3.7.5, Rowan's implementation of STON was updated to follow the spec when writing Association instances. As a result, the old version of STON support included in gt4gemstone is now out of sync and is missing methods necessary to serialize Association instances.