Unable to start the sub process from main process with same security settings

Hi All. While executing a process model having a sub process I am facing issues while starting the sub process. Both the parent and child processes have the same security settings in terms on initiator etc.and the user with which I am trying to run the process model has been mapped properly to the role. The error which I am getting is - "The user does not have privilege to the process that the activity attempted to start.". I even tried with both the options for Sub-process inherits security from parent process (unless overridden). Any thoughts

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