Raspberry Pi: Not enough memory on the target to process the packet: EXT_SELECT_SIGNALS

I would like to count colored objects with a Simulink-model running on a raspberry pi model B. I am using three video viewers to show the identified objects in red, green and blue respectively. While using only one viewer (e.g. only for the red objects) is working perfectly, using two or more doesn't show any output on the viewers and brings the warning "Not enough memory on the target to process the packet: EXT_SELECT_SIGNALS". Does anyone have an idea why this is happening and how to solve the problem? I will be grateful for any help you can provide :)