Hi Islam,
I had the same problem when running optimisation problem from cplex in matlab. However, the problem is not in cplex itself, but the memory in matlab I guess. Check whether you have very large matrixes that you can convert into sparse ones or any other initialising problems before it comes to the optimisation step. "-8" I can interpret as running cplex without any matrixes (or equivalently with [] matrixes) which yields to an outcome [].
Let me know if that the case!