Exception in MOA, when trying to use weka filter

Question

I am doing a science project on my school, and I need to use several filters on my data stream. I am using MOA with filters from WEKA. The following code is part of a classifier I made so I could use the Filter with a MOA classifier. I am ware that MOA has the WEKA classifier, where I can choose filtered classifier. However I making my own, to make sure the classifier is not testing the synthetic instances.

    @Override
public void trainOnInstanceImpl(Instance instnc) {
    Instance aux;
    Instances  moaNewInstances;
    weka.core.Instances mWekaInstances, mWekaNewInstances;

    mWekaInstances = new weka.core.Instances("WekaInstances", mAttFastVector, windownSize);
    mWekaNewInstances = new weka.core.Instances("WekaNewInstances", mAttFastVector, windownSize);
    moaNewInstances = new Instances("moaNewInstances",mAttList, windownSize);

    if(IsFirst)
    {
        getAttributes(instnc);
        moaInstances = new Instances("moaInstances",mAttList, windownSize);
        IsFirst= false;
    }



    if(cont < windownSize)
    {
        moaInstances.add(instnc);
        cont++;

    }
    else
    {

        cont = 0;
        mWekaInstances = converterToWeka.wekaInstances(moaInstances);

        mFilter.setInputFormat(mWekaInstances);

        mWekaNewInstances = weka.filters.Filter.useFilter(mWekaInstances, mFilter);

        moaNewInstances = converterToMoa.samoaInstances(mWekaNewInstances);
        moaInstances.delete();


        for(int i = 0; i < moaNewInstances.size(); i++)
            mLearner.trainOnInstance(moaNewInstances.get(i));





    } 

}

Basically the filter will be applied whenever the size of the window is reached. in the lines mFilter.setInputFormat(mWekaInstances); and mWekaNewInstances = weka.filters.Filter.useFilter(mWekaInstances, mFilter);

However those lines gives an Exception. What could be the reason?