I think that correct Portuguese should have an article "a" before "minha":
"Eu não consigo encontrar a minha chave"
Both are correct. I hope this may help you: http://duolingo.com/#/comment/64947 ;)
Fair enough. In that case then, the sentence with the article should also be accepted as correct.
"I can not find my keys" and "I cannot find my keys" should be marked as the same answer.
What's the difference between posso and consigo?
Posso = I'm allowed to
Consigo = I'm able to