ATM Machines..! Who has written?

It was late night. I reached my home by a taxi. As the taxi driver did not have change, I asked him to park at a near by ATM. I came running to the ATM Machine to draw some hundreds. Here goes my interaction with the ATM:
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Enter the card no: xxxx

Enter the Amount: 400

Choose Type: Saving Account

Confirm: OK

Output: Error: Please enter amount only in multiples of hundred (100).

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I repeat the same use cases multiple times but, the output is the same error message. Even, I cross checked many times whether 400 is entered correctly. I am totally confused myself, whether 400 is divisible by hundred or not! Then, I couldn’t understand why the error message was displayed. I ran to another ATM, and I was getting some other error message there. Error: You have exceeded the maximum limit. (I have not drawn any money using my card for the last two days). Are the machines gone drunk?

Whenever, the ATM machines are ‘out of service’, I am not upset. Because, there might be ‘N’ number of reasons. It is agreeable. But, when they display such misleading/incorrect error messages, I easily get tensed. I am searching for the guy, who has written that kind of software.

It is not that, only the functional deviations are bugs. Also, if a system does not handle a error situation, or does not display a proper error message, then that is also a bug. It is a serious bug, at customer perspective. Leave the customers aside. Just few questions to the guy, who has developed the ATM software:

1. With this incorrect error message, how will you find out what has gone wrong/failed in the system?
2. Without knowing the actual failure, how are you going to fix it?
3. What do you think, either an end user (me), or the bank people can react to the incorrect error message?