This error can be caused by a redirect in the Participant Center set up. 

First determine what Participant Center the TeamRaiser is using. See Where can I view/change the Participant Center in the Teamraiser? Then: 
  1. Select Fundraising > TeamRaiser
  2. Click on the Participant Centers tab
  3. Click on Edit for the Center in question
  4. Click on step 2, Configure Options
  5. Check for a redirect on 1, Participant Center Home Page. This box should be blank unless you have the Participant Center embedded in a PageBuilder page