Hello Muhammad Farid,
this kind of errors happen when the system parameters not adjusted properly.
Binary output should be connected to binary input,
Electrical output should be connected to electrical input,
and Optical output should be connected to Optical input,
I want to add that if you are using fork you can connect in cross of the above three type of signals. i.e. using fork you can do so as a fork accepts all kind (the above mentioned 3 types of signals). But in terms of cross signal connection while execution it will definitely show error as you have not properly connected. Think it logically about the signals and the connections.
For knowing the signal type just do double click at the input/ output port and you will see the type of the signal.
Regards,
Dhiman