What is the difference between "Arigato godzaimas" and "Arigato godzaimashta"?
「ありがとうございます　と　ありがとうございました」

Question

What is the difference between "Arigato godzaimas" and "Arigato godzaimashta"? 
「ありがとうございます　と　ありがとうございました」

Answer

（Domo） Arigatou Gozaimashita (どうも）ありがとうございました　is in the past tense all right. But when you say thank you automatically  it is a past tense. Don't you think so?

Grammatically speaking you're suppose to say ありがとうございました but there's no problem in saying ありがとうございます　either. Oh, by the way, sometimes I only use domo （どうも~）.

Answer

grammatically, the second one is in the past tense. I don't know if it has a subtly different meaning or not.