Usually it means you have too many sub-calls -- probably a method calling itself or two methods calling each other.

This error doesn't appear frequently , sometimes at the start of execution , but usually it appears spontaneously .I dont't have recursive method or methods which calls each others . It started to appear today , but I didn't add any method to my code .

Yeah, it did not appear to be recursion at your code level. It would be difficult to suspect a problem with the collision checking code of greenfoot, however. Sorry, I cannot be of much help on this one. Maybe a greenfoot team member can shed some light on this issue.

Are there any more lines in the stack trace? It's possible there's an error in the collision checker because it does use recursion but the stack overflow will probably involve more than three calls, so we'd need to see more of the trace. If you're willing to, zipping up the scenario and sending it to support@greenfoot.org would allow us to take a look.