Hi BarneyArAldi,
this error message can be confusing even to experienced programmers.
Unfortunately you didn't provide enough context, code and - most importantly - the error message for any of us to understand what is going on.
You may want to tell us what the code the error occured in was supposed to do, what the function was and what error message you got said. In addition to that saying what you've already tried to solve this issue might be helpful for us as well.