getting exactly same error - something has broken in March Release. Someone in Microsoft needs to look at this urgently - this is breaking all embedded reports.
Multiple people are reporting this.
Also posted at http://community.powerbi.com/t5/Issues/Error-Feature-switches-have-not-been-registered-yet-so-switch/idc-p/141869#M4404
https://community.powerbi.com/t5/Desktop/Feature-switch-instance-is-not-initialized-yet/m-p/139350