PowerPivot Refresh Issue in SP2013

Getting the following comment for a PowerPivot Data Refresh in SP2013:

'The schedule has been altered outside of PowerPivot.  Use the Manage Data Refresh page to update and re-save the schedule.'

This is plaguing my farm.  It runs one day and not the next.  No clue what is causing this.

Any ideas? Help appreciated,

Doug Schultz