Unable to trigger sub process from guest "Started By"

Hi Folks,

i tried to trigger process model from mail(External system) using UUID. The main process gets triggered by guest but i have one sub process inside it which is not getting triggered. 

Please find the error below and attachment for error screenshot.

Problem:  The user does not have privilege to the process that the activity attempted to start.

Details: 

Recommended Action:  The process is not started, and this node cannot complete. Please start the next node if necessary.

Priority of this problem: High Priority

  Discussion posts and replies are publicly visible