Those using Google Audio ads are reporting that there are some problems when resuming ads. If a campaign is paused, you apparently cannot resume it. If a campaign is stopped, you also cannot resume it. Another issue that was reported is that some advertisers cannot run their audio ads on more than one station.
AdWordsPro.Steph writes a response on the Google Groups thread and says that you're unable to resume a campaign once it's stopped. You can, however, copy your settings over to a brand new campaign and start again.
The other issue reported are likely to be technical glitches, Steph continues. Her recommendation is to report it as a bug to the attention of the Audio Ads team.
Forum discussion continues at Google Groups.