You have just received an email about the failure of the publication of one of your campaign, something like this:
Your account has reached the maximum number of ads allowed on one account (5000). Please delete some of your old ads to create new ones.
This means you have too many ads in your Ad Account, and since the limit is 5000 ads (or 1000 AdSets) you need to free some slots for the new-comings. What you need to do now, is simply deleting some of your old campaigns (if you don't know how to do it, look here!).
Once you have done it, you must try the publication again, which consists on going on edit mode (or click on the link you received via email) and reach Step 5 for the publication.