We can't tell from only that and you don't even say which FEX code.
The first expression p might be an array but x,y are while not illegal, somewhat unusual variable names for array indices; sure it isn't a missing function?
In the second, it's pretty clear that Zernikmoment(BW2,4,0) is being interpreted as an array reference instead of a function which would tend to indicate you either haven downloaded the full submission or got it installed in a location on the Matlab path so all the m-files are being found the submission needs.
