A long time ago, I was told that I am a Type A blood type, and a carrier for Type O.?

Well, A type blood is dangerous for people with B or O type blood (not AB type).

Who told you first that you're Type A? And how did you know that you weren't 0 when you had kids? Have you been tested and found to be type A twice?

It's a myth that it's impossible for you to be 0 if neither of your parents were. I keep answering questions on here from people worried their parents/child can't actually be theirs. It's particularly frustrating that the answers they get often agree with this.

One of my previous explanations:

http://answers.yahoo.com/question/index;_ylt=Ags7o...

Generally, being a 'carrier' for type O would mean a genetic thing. As explained in my previous answer(s), we each have 2 alleles (gene versions), 1 from each parent, for our ABO type. A is dominant to O, so an A & O pair of alleles would give you blood type A just as surely as A & A would, but you would be a 'carrier' for O, meaning you could pass on an 'O' allele to your child. (So your child could possibly be type O, depending on what allele they get from your partner.) If that's you, having an A & O pairing of alleles isn't uncommon, and certainly wouldn't cause a classification error.

I think it's very unlikely that you are having your blood mis-classified. There are rare and chimeral blood types which I don't know everything about though, so I don't want to say that 100%. The best thing to do is probably to write to the blood donor people explaining why you think you're type A, not O and see what they say. (Again, don't tell them that neither of your parents had O type blood. They'll be used to correcting that idea all the time and it might mean they don't pay attention to anything else you say.) I imagine they'll be happy to answer your questions if it's likely to get you donating again.

If there's any way I can help, feel free to email me.

They will not give the wrong blood type to the wrong person. They have to type and cross the blood first. I have never heard of anyone getting the wrong blood. You are probably type O if thats what the centers are telling you.