No Error, No confirmation, No payment Process

I'm having a few users complain about not receiving conformation, or a success email after going through the shopping cart stage. There doesn't seem to be any rhyme or reason to it, and none of them show up as a processed transaction, but all of them report that they finish the process.

They don't report any error messages. Some report the following:

"A box came up and said only click once then cancel or it will process twice."

I can't see where this error comes up, and I have also tested in test mode and set values to $0.01 cent and processed transactions on my own card successfully. Is there anything I'm missing? Is this something that other users experience? Where would I get the "process twice" alert?

Any help would be appreciated as I need to use this to have students register for a class.

Thanks Chris,

Here is the URL: https://www.mywineknow.com/class-registration-private/

(I've set one of the items to a $0.01 while I test on live accounts)

Thanks Chris I'll send an email right away.