Since ODE 0.13 it has not been possible to use ODE from multiple threads. Currently, this causes nasty errors in the rwsim_tasksimulation-test where 2 threads are used. I have located the change in ODE that breaks the multi-threading (revision 1878):
I think it might be possible to fix the error by calling dWorldSetStepThreadingImplementation, but I have not been able to find any good documentation on how to do this. It appears that ODE wants to control the creation of threads, which is somewhat different from how we do it.