PsN Stop: Out of memory.

Dear all, I am conducting a scm search of covariates using PsN. The model uses ADVAN6 with FO estimation method. Due to the complexity of the model, it crashes after 13 rounds of running with an error message saying: out of memory! The scm uses a parallel processing of 5 CPU cores. At the beginning of the model we stated $SIZE as below: $SIZES LIM6=3224 LTH=70 LVR=20 NO=1000 The base model has 15 thetas and 8 ETAs. After 13 rounds of scm, the model has 38 thetas, which is well below LTH. After checking the last run, all the NONMEM RUNS were finished in the m1 folder. I was wondering if anybody has encountered such a problem before? Is this because of inappropriate resource allocation, or because of the memory shortage? Actually, I am not even sure whether this is because of error in PsN, or error in the NONMEM itself. Some other details of the model: 1. scm file investigates effect of 5 covariates on 8 parameters (5*8); 2. NONMEM is ver 7.2. Many thanks for your kind help. Best Regards -- Xinting