Are your board's login credentials incorrect?
If the login credentials for your individual Job boards have been entered incorrectly, you will receive a report to say your ad has been undelivered.
It's quite easy to check the reason for these posting errors.
You will notice it says 'help' next to the status column if an ad has been rejected.
Just roll your mouse over the yellow alert icon, and you will see the reason why the ad has not been delivered successfully.
It will also offer you instruction on how to resolve the issue.
Go to 'Job boards and Quotas' in the left hand menu, and select the 'Settings' tab for each board.
You may then update the login credentials for each board as necessary.
Credentials Update article can be found here.