sounds like my bank, bank of Montreal, they only allow 4 number passwords for their e-banking shit (seriously)
(Unfortunately, this reads just as valid sarcastically as seriously).
http://www.bmo.com/home/about/banking/privacy-security/prote...
Maybe your the victim of a Phishing attack or something, for example maybe a fake site told you you had to use 4 digits.
Honestly I've heard of a lot worse then this:
http://www.bmo.com/home/about/banking/privacy-security/how-w...
What i dont understand is now all bank cards in Canada have a smartcard embedded, why cant they just hand out $5 card readers and use that for ebanking, every major browser and OS supports this stuff right out of the box.