We had major problems one year on a credit card of my dad's. I think it was a Tesco Finance one.
We went to the malls and there is 3 of us kids and we all wanted new clothes. So we went to all the popular ones, Abercrombie & Fitch, Hollister, American Eagle etc. So we made a few transactions then I go to purchase a few things in Aeropostale and this was about 3pm on a weekend. What happens, 9th transaction so the card is blocked. The shop had to call the bank to try and get it authorized which at 8pm on a weekend is a hard job to do. Finally, after 1hr it was authorized for $60 but if it was $6, $60 or $600 the transaction wouldn't have gone through. We had to call the UK the next day which cost £27 (got it back) to unblock and so they wouldn't do it again needless to say the person on the other end was not helpful at all.
Another year we were paying points and money for the hotel at OKW. We try to pay for it on the card, wouldn't go through and getting through to the UK at 3am in the morning is even a harder task. Used a different one and it went through.
In future now any credit cards we plan to use abroad, we tell them just to be on the safe side.