politeness - Difference between 「来ませんでした」and「来なかったです」

Possible Duplicate:
Is じゃないです equally correct as じゃありません?

Both have the same meaning ("did not come") and according to my Japanese co-workers both are acceptable while they can't define the difference.

What is the (possibly obscure) difference in meaning between these two sentences?

Answer

Not exactly the same question, but the answer applies as well:

Notes