Hi there
It's very hard to tell what the problem is from the screenshot -- but it is a common error when I work! It would be helpful if you could post a piece of the list that is causing the problem. You can subset a list with square brackets, so
dput(your_list_name[1:10])
would make a text version of the first 10 items in your list. Then post the code that you are applying to that list that is causing the error.
This FAQ provides more information on making a reproducible example