How to assign task from one user to another?

The Requirement is to assign the task from one user to the other user.
Scenario :
The task has been assigned to a group.
I(say 'Sam') am accepting the task, now I have opened a new tab and as per the requirement I'm reassigning the same task (which I have accepted) to the new assignee(say tom).
Now I(Sam) am trying to submit the task an error message displays saying "Task Cannot Be Submitted. You are not owner of the task" (This is expected).
But in another environment when the same is replicated an error message displays saying "An Internal Error has Occurred. The Page Could not be loaded [HTTP Code = 403] (APNX-1-4279-001)".
Any Idea why this is happening in other environment, please help me out.

Thanks in Advance.

OriginalPostID-201170

OriginalPostID-201170