Recently I’ve been using the Google Analytics API to automate some of the report generation I’m doing.
After some serious hair pulling I finally realized that there is a bug in the API when one of the metrics you request is adCost.
Specifically, when requesting adCost with other specific metrics, the results for adCost are always zero.
After some research I found this post which confirms that Google is aware of the adCost issue.
Unfortunately the post doesn’t really help much in terms of finding out which combinations trigger the bug, so I tried out some of the combinations myself found that using any traffic source dimension with these metrics will trigger the bug:
- entrances
- exits
- exit %
If you are aware of other metrics that trigger this bug, please let me know and I’ll add them to the list.
I should add that this bug also affects custom reports!
If you’re using any traffic source dimension and adCost together with any of the above metrics in a custom report you’ll get zero for the adCost data.
Hopefully this saves someone else from some major hair pulling.
Analytics Impact 
Thanks for the update ophir. Also, in the rare cases that I use the navigation summery report I also get the same result (%exit=0). do you think it might be connected?
Can you send me a screenshot to see what you mean?
You can send it to ophir.prusak@gmail.com
This problem is still current as of 2011/02/21. Google recently expanded their reporting to allow for more combinations with ga:visitor, but this remains unfixed.