In the checkout pages that are created with the checkout wizard the selection in the country menu will be United States, but the value is set to US, here is the code from this option in the country select list:
<option value="US">United States</option>
Was yours different from this?
As for the error you are now getting this is an issue with the Universal Email implementation within eCart, to resolve it you will need to update the following. Currently in the UE code that is on these lines you have this:
$BurstSize = undefined;
$BurstTime = undefined;
$WaitTime = undefined;
You should update these lines so that they are like this instead:
$BurstSize = 200;
$BurstTime = 1;
$WaitTime = 1;
This should stop the error that you are getting when you get to this page. I have logged this issue as a bug so that it can be fixed in a future update.