Fitnesse: Clicking Anything

Hello. I am using Fitnesse and cannot get the computer to click on anything. I will describe my process. I log in to the site where I want the computer to go, go to Developer Tools, and find the name of the button I want the computer to click on. So using the cheat sheet, I try to have the computer click on a button (click on buttonBUTTON_NAME or BUTTON_NAME[INDEX]), but it never works. Nor does it work for clicking on links, or cards, or grids, etc. I always get this error: Could not invoke constructor for ....."

Help, please. 

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