Errors and warnings are based on each publication's specifications on how they want to receive their files.
Warnings are not too critical and can be approved by you.
However, Errors, which are highlighted in red, must be fixed.
The pre-flight file report provided by Adsend gives you all the information you need to make your decision and correct any Errors. If your pre-flight check fails, you will have the opportunity to download the Advance File Report which provides detailed information about why your file has failed.