Abaqus single cpu and multiple cpus

Dear all,

        I am running a abaqus job to simulate the failure mechanism of a pile-foundation system. The material used is mohr-coulomb soil. I found that if I use multiple cpus for the calculation, I got different results each time (at the step which does not converge). However, If I just use single cpu, there is no such kind of problem, each time I got the same results.

         Anyone else has this experiences before? I am quite confused.

 Zheng Li