Hello,
Please note, that this warning isn't linked to your previous issue.
If I'm right this error isn't a problem to run full checkout process, and his just the results of a specific configuration.
The most simple is to switch on "None" your Error Reporting, like it's strongly recommends for an online website.
But of course if one day trouble appears it will be useful to switch it On (System Default).
to reach this option :
- go to System => Global Configuration and click on Server tab
- In Server Settings look for Error Reporting and select among several value (now on None)
And so I switch it off for you and from now, this warning won't appear again.
Regards,