Is it not possible to call a Matlab .DLL from .NET in parallel?

I have a compiled Matlab DLL called "GeneticAlgorithmOptimizer.dll" with a class/method "gaOptimizer.optimize()" that uses said algorithm to generate a solution based on some input data and parameters. It takes about an hour to generate the solution.

I would like to call it in parallel through a .NET application like so:

            List<bool> boolList= new List<bool> { false, true };
            Dictionary<bool, double[]> matlabSolutions = new Dictionary<bool, double[]>();

            Parallel.ForEach(boolValueList, (boolValue) =>
            {
                var inputData = dataGetter.getData(boolValue);
                var parameters = parametersGetter.getParameters(boolData);
                var opt = new gaOptimizer();

                % THIS IS WHERE THE MATLAB DLL IS CALLED
                result = opt.optimize(inputData, parameters);

                lock (matlabSolutionsBothPools)
                {
                    matlabSolutions.Add(boolValue, result);
                }

            });

However, the calls to Matlab end up happening in sequence rather in parallel. The first one has to complete before the second one starts.

Is this a limitation of Matlab? Does anyone know a way around this?