Unable to create links between sample population and constraint tables

[SEAsoN8599]

Hello.
I tried to set up a model configuration. The first step would be creating links between sample population and constraint tables. But I did exactly as the guide book told me to do without getting the desired effect. I locate the sample population table in the data source, left click to highlight it and while keeping the left mouse button pressed drag it to the population area of the microsimulation screen and release the mouse button.
But the fields from the population table were not displayed in the ‘Field’ Colomn.
I tried many times. But it just cannot work. Without the link, I cannot proceed with the following work. I am really upset.
Could you please tell me what I can do with the situation?
Thank you for your time.