"Señor, ¿usted conoce a la secretaria nueva?"
Translation:Sir, do you know the new secretary?
In the above sentence, yes. As a sign of respect, we call men "Sir."
Small children address men as "mister" sometimes: Hey, mister, can I pet your dog?
Because those are past tense, whereas the Spanish sentence is given in present tense. Yes, they amount to practically the same thing, but this is more or less a computer program so it can be a bit picky.
Do you mean that the latter is past tense and the former isn’t or are both past tense? The first one is accepted though and the other one not, that’s what is puzzling me. Could you explain it a bit more, please?