having trouble with spatial filter in provided BCI examples

[rainydhiya]

hi all,
i run the bci examples provided by openvibe,
ssvep-bci-0-acquisition-test.xml,
it return the below error,
as i'm not familiar with openvibe,
can someone explain how to configure this box accordingly?

[ ERROR ] At time 0.469 sec <Box algorithm::(0x00001bd0, 0x0000133b) aka Average> Bad matrix size - Expected 6 input channels and received 16 input channels
[WARNING] Box algorithm <Average> has been deactivated because process() function returned error