Actually, I remember hitting something like this not too long ago. It turns out Marriott passwords are CASE INSENSITIVE! I get so frustrated by sites coming up with password rules that you must write passwords down to be able to remember them if you don't use them everyday.

I just tried three possibilities for my password, as entered, all upper-case, and all lower-case. Even mixed case worked! They all allowed me into my account.

I guess that goes along with their process of flagging my account because my email user name is Marriott. I was told I can't use that... ummmm