Validation email not working with CB integration

I have a two issues actually, please a general narative to see if i did this the correct way.

So I have CB installed and wasn't sure if I should redirect to CB for new user signup, or create custom fields and map those extra fields to the CB ones so that the full data is collected on new user registration. I did the later with the custom fields in Membership as the previous wouldn't catch the billing part of membership which I was hoping for - therefore turned off the CB redirect plugin. I hope this is the correct method.
So the issues:
1) using the Membership signup form, the date field which I want them to complete enters a timestamp instead of just a date. When I pass this value to CB it fails and doesn't record it due to the mismatch. How can I control that it is just a date and not a timestamp and in the format I want (month/day/year). Is there a server file to edit?
2) when the user completes the registration form and pays, the following error message is displayed (see attachment).

Thanks very much.