Every campaign in Post Affiliate Pro can have 3 different statuses, so let's explain them a bit.
Active - can be promoted by the affiliates so they can earn commissions under it.
Paused - campaign is visible to affiliates in their panels and they can potentially promote it, however it will not track anything under it. Clicks on banners of such campaigns will not generate any affiliate - visitor relation and therefore the visitor will be unreferred and his orders will not be tracked normally. If there were clicks saved on such banners before when the campaign was active, then it could save a sale but not under this campaign, instead it will try to select the default one. If the default is paused then it won't save.
Stopped - similar to paused campaign, however stopped is completely invisible to affiliates so they cannot see its banners and links.