There's most likely an error in your DTM code. You can use the Chrome extension here to troubleshoot your DTM configuration: http://help-forums.adobe.com/content/adobeforums/en/marketing-cloud-forum/adobe-marketing-cloud.topic.html/forum__lkzf-_dtm_switchdt.html.
In addition, there are fantastic videos here which walk you through the setup of DTM and the configuration of the Analytics tool within DTM: https://outv.omniture.com/ (under Dynamic Tag Management)