Microsoft adCenter has editorial policies that prevent a lot of ads from being shown.
For example, the keyword "[adult video]" can't be bought. At least not by me.
Anyways, it's important to check the reason for rejection - especially when the rejection applies to your AD / KEYWORD combination. If you understand what's not allowed, it makes it easier to write ads the next time.
Like many of the adCenter screens, the Rejection Reason interface is poor - because it only lists 5 rejections at a time (imagine clicking through 600 rejections that way). However, my helpful adCenter QuickLaunch rep, emailed me the following instructions for getting a CSV report listing all rejections at once:
You can get a bulk download of your rejection report by clicking on the Reports tab once you are in adCenter. Once you are in there, please select rejection summary in Report Group, choose a report view and date range. You can then customize the report by clicking on the "Customize this report" link then run report.
For reference, here are some of the reasons Ad/Keyword combinations can be rejected:
This is MSN lameness, since the landing page was mostly images that were relevant
I accidentally typed two exclamation points!!
Here's where adCenter's 3 keyword parameters can come in handy - you can fill in a parameter field that's short enough to fit in the ad text
This was a trademarked keyword
Another mistake by adCenter - the site was very relevant.
Another over-zealous restriction. I think they flagged the abbreviation "sm", as in "Small', but they think it's S&M or something.
Who knows? I couldn't tell which guideline triggered this.
Despite some glitches, and it's inability to handle mostly-image landing pages well, I actually like this system - giving a reason is something MSN adCenter does better than AdWords (though in general, AdWords is way better to use for big accounts).