SWIG's generated tracking code is not compatible with the latest ruby versions : 1.8.7 and 1.9
Specifically, during ruby's garbage collection phase, the function SWIG_RubyRemoveTracking may be called, which in turn calls SWIG_RubyPtrToReference.
This converts a void* (ptr to the C++ object) to a ruby numeric corresponding to the pointer address, which is then used as a ruby hash key. The pointer address may convert into a Ruby BigNum, which is a new object allocation. As of Ruby 1.8.7 / Ruby 1.9 object allocation during GC phase is a bug and will crash out with an error message.
For the time being we (wxRuby) have worked round this be re-implementing the tracking code using a HashMap class from wxWidgets, but this isn't a general solution. This problem will affect any SWIG/Ruby project that uses the tracking code.