This means that the software is being asked(by You) to repost the exact same ad(s) that currently exist on craigslist in that exact same category and city. By default, the software will not repost these ads until the previous version of the ad is removed from craigslist. There is good reason for this. By RE-posting the exact same ad while an older version of that ad is still on craigslist, you run a high risk of being flagged or blocked from craigslist. There are two options here:
1. Purchase the auto-repost addon which will automatically delete previous versions of ads from craigslist BEFORE it RE-posts the ad.
2. Change your settings to ignore this and post the ads anyways, risking being blocked. To change this setting, open craigslist.exe.config (it is in the program's folder where you installed the software) with notepad. Change default value "0" to "3" here: