Hmm, well it mean that the given line do not have the right indentation level.
Code:
Indentation level 0
Indentation level 1
Indentation level 2
[...]
But there's something weird with your code screenshot.
The faulty line is at the same indentation level that all the other lines,
but the symbol in top of the line seem to indicate that it's a block that can be folded :/