The error you are getting means that the item specified in your selector is not being found for whatever reason. If you go to edit the selector on the activity that is breaking, does it validate? If so, does it validate again after refreshing the page?
If the selector doesn’t validate, try clicking on “Repair” in the Edit Selector window and re-indicating your selector, then try running/debugging the code again
Enable simulate type under properties of type activity
Enable wait for ready property to Interactive. Sometimes field takes lil long to appear on screen and if bot tries to type in value that time, it might fail.
Thus enabling these properties helps ensure element is typed into properly.