This uncommitted work error message, is driven by Summer 15 release as seen here: http://salesforce.stackexchange.com/questions/77118/pagereference-getcontent-hit-exception-due-to-summer-release-15, We've made the adjustments to avoid these issues going forward. Please upgrade to the latest version of the Report Scheduler 3.0 or greater. You can do so by following these instructions: 

  1. Go to the AppExchange
  2. Login with your standard Salesforce credentials
  3. Go to the smiley face in the upper right navigation
  4. Go to My Accounts, Report Scheduler
  5. Click on Update Available