Predicting text data labels in test data set with Weka?

I am using the Weka gui to train a SVM classifier (using libSVM) on a dataset. The data in the .arff file is

@relation Expandtext @attribute message string @attribute Class {positive, negative, objective} @data 

I turn it into a bag of words with String-to-Word Vector, run SVM and get a decent classification rate. Now I have my test data I want to predict their labels which I do not know. Again it's header information is the same but for every class it is labeled with a question mark (?) ie

'Musical awareness: Great Big Beautiful Tomorrow has an ending\u002c Now is the time does not', ? 

Again I pre-processed it, string-to-word-vector, class is in the same position as the training data.

I go to the "classify" menu, load up my trained SVM model, select "supplied test data", load in the test data and right click on the model saying "Re-evaluate model on current test set" but it gives me the error that test and train are not compatible. I am not sure why.

Am I going about this the wrong way to label the test data? What am I doing wrong?