Not accepting a resolution below 640x480

I am trying to deploy a Simulink model to the BeagleBoard XM that has an output dependency on the size of the resolution. Ultimately if I use 640x480 the model doesn’t even run on the BeagleBoard. To try and make it work more efficiently I reduced the resolution to 320x240 but when deployed to the BeagleBoard the HDMI screen I am using immediately goes black and nothing happens.

Is there some sort of setting I need to change to allow me to deploy with smaller resolutions?