I had a problem that sounds very similar to this while trying to purchase an Alsa (Spanish bus company) ticket online using a Mastercard. I tried using Mastercards from 2 different Canadian issuers and neither worked. Since I needed to travel the next day I said the he_ _ with it and took the train.
Logically it would seem that the problem was with the merchant, because I have used the same credit cards for purchasing tickets online from numerous other European plane, train, and bus companies with no problem.
There is a fairly detailed page on the Tiger website;
http://www.tigerairways.com/home/vbv_mcsc.php
discussing the use of Verified by Visa and Master securecode, but it sounds like it is supposed to work whether your credit card has these security features enabled or not ?
Any other wisdom on this subject would be greatly appreciated, as I may be wanting to purchase Tiger Airways tickets in the near future.