segmentaion fault with array[4096]

hello,

because I want to do some tests with fusion/RTAI on my mpc852,
I had to downgrade my system to kernel 2.6.10
And I get a strange problem: if I start application with char array size
4096 (or even smaller 2600) I get "segmentation fault".
Could someone gives me a hint? Is this kernel configuration problem?
Where can I start looking for a reason?

thanks
Pawel