Hi Ryan,
The problem I believe is that you are trying to track the specific page, rather than the entire domain (Of course I understand why in this case), but the feature is configured to track the domain and will therefore not accept a URL that includes the path following the trailing slash. Basically, it wants you to just enter http://en.wikipedia.org
I am not sure if SEOmoz staff will have any suggestion on solving this issue for your campaign, but you should email help [at] seomoz.org explaining your problem. Since it is a holiday weekend, you may need to wait a little while for a response, but I know that SEOmoz staff constantly surprise people by responding to enquiries when we don't expect them too, so give it a go. A direct email will definitely be the quickest way to let them know you have a problem.
In any case, while you cannot pull the information into your campaign, you can still obtain it using the Open Site Explorer tool. I ran your Comparison URL in Open Site Explorer , but there is insufficient data for this particular page so you will only see the domain information at present. You can find all of the information that is returned in a campaign using this tool. To compare with your own site, just click the "compare sites" link below the OSE search URL input, enter your own URL and then run the search.
You can also download the comparison report from OSE and run advanced reports if you wish to do so. Export to CSV and you will be able to utilize the information in Excel, or generate a PDF.
Hope that helps,
Sha


