Can't withdraw my steem

Hi everyone, I have a question:

I can't withdraw my STEEM for some reason. I put in the memo I get from bittrex and put in my password, but then it says I have a wrong active key. But putting in the active key (which is different from my password) doesn't work either, cause it says that it's not a long enough password. Does anyone know, which of the keys I get do I need to put in in order so send some STEEM?

Thanks for helping out...!