Cannot send session cache limiter

Hi I'm new to the list, but I've been PHP programming for almost 2 years now, hard to believe. Anyway, I have a program that's giving me a "Cannot send session cache limiter", yet the very first thing the program does is session_start(); The only thing I can think that's different about this program to others is that it calls itself. For instance, it outputs a form, the user hits 'submit' and the form action is the same prog .. there are two or three stages handled like this. I think that's pretty standard, right? The error only occurs second time around, not when I arrive at the program from another. It feels like something at the back end is saying "well, your next program is the same as your current one, so I won't bother resetting anything", leading to the error when session_start(); is called the second time around .. as if I'd issued session_start() halfway through a program. I'd look it up, but, err, what under? Can anyone shed some light? Cheers J