Why, running Timestamp block in external mode is throwing an Error in S-Function?

I want to use the Timeout concept in Simulink and flash the model to raspberry pi. I am using the Timestamp block to connect it to the CAN Timeout Detection block. I am running the model in external mode to test for the operation. When I run the model, an error is been displayed saying, "Error in S-function '../Timestamp': Unable to acquire handle to MATLAB function 'sldrttstamp'". It is mentioned as the block performs in external mode, but still I am getting this error. Also please guide me the alternatives to achieve the timeout in external modes.