In Germany, many of the ATMs were in enclosed vestabules that required a card to enter. Some seemed OK with any bank or credit card, but others apparently needed a specific card (the bank's ATM card, I presume).
In Koln, we were in a hurry to get money to catch the train to Munich and the Dresdner Bank was the one closest to the hotel. It is in the latter category, neither my bank card nor my credit card would open the door, even though I was fairly certain that once I was in, either would work in the ATM. I didn't really have time to run around looking for an ATM, so I pulled out my wallet and started trying every card I had. I finally found one that worked: my BYU ID card. I have no idea why it worked and nothing else did.