How can I display different images on different axes in the same GUI?

I'm using MATLAB R2012a to develop a GUI for manual medical image segmentation. In particular, I want this regions to train a classifier for automatic brain tissue classification.

The GUI I design contains 2 axes, with tags 'figureImage' and 'figureVOI', respectively. In the first one I want to display a single slice of a 3D MRI scan, and in the other one I want to show the mask associated to that slice. I allow the user to move between slices using a scroll bar.

I'm using a 3D matrix to represent the image ('image'), and a 3D matrix to represent the mask ('voi'), both of them in the handles structure. I initialize the 'voi' matrix with zeros when the GUI is loaded.

The code I applied when the user clics on the scroll bar is the next:

    % update the number of the actual slice
    handles.actualSlice = round(get(handles.sliceSelector, 'Value'));

    % update the image and the mask
    axes(handles.figureImage)
    imshow(handles.image(:, :, handles.actualSlice));
    axes(handles.figureVOI)
    imshow(handles.voi(:, :, handles.actualSlice));

However, when I clic on the scroll bar, the GUI just scroll to cut nº 70 aprox., and then all then the GUI stops to update the axes. If I close the window and try to run the GUI again, and MATLAB shows me a system error.

I want to know what I'm doing bad, and if there is another way to do what I need to do. Thanks a lot! :)

[Image Analyst]

Coy and paste the error back here.