On MPC8250's interrupt number 0

I have two questions ask for your help.
Our new product heavily use MPC8250 developped in Tornado II with
vxWorks 5.4 and GNU CC.
1)It get too much and steadily increasing interrupt numberred 0. From
MPC8260UM/D 05/2003, REV 1 the interrupt source description of
interrupt number 0 is "Error (No interrupt)" and "The error vector is
issued when no interrupt is requesting service." So, Is the phenomenon
we meet correct? And if the key is "No" what is the cause and how to
avoid it? We have tried to disable it but failed.

2)Our system reads from the SDRAM too slowly. And do you think what
causes it? especially, Is it possible for BSP configured incorrectly
to bring up this result. By the way our MPC8250 is not equipped with
L2 cache.