I just tried it with some GA data. It seems to be picky about what metric you join it to but ga:pageviews works. Both ga:campaign and ga:pagePath are dimensions and you need to join them to a metric. You can reference GA documentation here regarding what are the valid combinations. As an example, I managed to retrieve a really long report using (replace with your profile id):
https://www.google.com/analytics/feeds/data?ids=ga:123456&dimensions=ga:campaign,ga:pagePath&metrics=ga:pageviews&sort=ga:campaign,ga:pagePath&start-date=2009-01-01&end-date=2009-06-30
Hope this helps.
megeria
2009-07-01 23:49:52