Removing the extra include is fine but you should not set the redirect like you have done. Rather than stop the error from occurring it seems that your redirect is just getting the user to the next page before the code that causes the error runs. You should undo any changes that you made to the redirect.
The error you are getting is a MySQL error and is being reported directly from your db. This tells me that there is a problem with the values you are using on this part of the checkout. What type of checkout did you select and have you made any changes to the page? What about the data types of the information that is being stored? I have seen errors like this when the information is not of the rite type, missing, or referencing non existing values.
To determine what the problem may be you should print out the query so that it can be examined further. I have added some debug code that should print out the query so it can be looked at in more detail. I added a die() statement just after line 292 in the page that you posted. Please run a test with this page and let us know what the result is.
Also, you should update your Universal Email code on the page, currently in the UE code that is on the top of the page you have these lines:
$BurstSize = undefined;
$BurstTime = undefined;
$WaitTime = undefined;
You should update these lines so that they are like this instead:
$BurstSize = 200;
$BurstTime = 1;
$WaitTime = 1;
