Warning: session_start()

I'm a bit confused......
I've had a site up and running properly. Than I had to delete the whole content. I've uploaded the SAME content again and now there's a line at the top :

Code:

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Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /var/www/include/form.php:160) in /var/www/include/session.php on line 41

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I really haven't changed any content regarding sessions so I'm confused... :confused:
What went wrong? Server side issue?

Session_Start() needs to be before ANY output - including HTML, text, whitespace, anything.

If you look in the HTML sourcecode, you'll see where abouts that error is. You'll probably see that it's after something. You need to move that session_start so that it is before any output.

okay, that's clear to me. BUT how can happen that everything is working fine and then the SAME content and this Warning?

Furthermore : I have the EXACTLY SAME site at another server where it works perfectly without any warnings....