Problems with login, checkout, and downloads

[freya]

I don't know how to recreate this. It's happening with my customers. They will try to create an account and be kicked out to the beginning of the process again. Or they will manage to create an account, but won't be able to continue all the way through the checkout. Or they will purchase a book only to have it be corrupt when they download it, but the original file is not corrupt. It does not matter whether the file is zipped or not. (Matter of fact, I seem to have more problems with zipped files than those that aren't.) These are people who purchase electronic goods online frequently or who have purchased through us in the past and never had problems only to be unable to download, receive a corrupt file, or be unable finish the process of checkout.

From what I hear from the public, I believe this is happening about 30% of the time.

I have looked at my logs and found that there are some 5600 pages not found in the https in one month -- all dealing with the login/checkout even index.html under https (although I don't necessarily have the index of my store in https, I do have the login and checkout in https).

Although I am considering that it may be a host issue, and I know I need to update the carts to the newest version of Zen Cart, I don't want to do it at my current host only to have to do it again at a new one, should I go that route.

Does anyone know what could cause this?

Thanks,

Marci