PowerPivot for SharePoint scheduled data refresh does not work for the first day of the month, an error is generated every two minutes. ULS shows:
PowerPivot Service Data Refresh 99 High EXCEPTION: Microsoft.AnalysisServices.SharePoint.Integration.DataRefreshException: The data refresh job failed because it did not run within the time period allotted for running this schedule
This looks to be a software defect.
If you refresh the workbook daily, the first day of the month will refresh fine.
If you refresh on the second day of the month the refresh will work.
The product group is looking into this issue and it may be resolved in a future release.