I create an xml document with openxml and I am adding some cells as formulas

For all the created formula cells the problem is that if they call a function, they evaluate the arguments as one and that causes #### result in the cell

For example in vba modules I have this function

Function Function1(param1, param2, param3, param4)
   ...
End Function

And in the formula that is created by openxml

=@Function1(F14 CE14 M14 CG14)

but clicking show calculation steps I see that the 4 arguments are evaluated as one

@Function1(#NULL!)

and that causes #### result

Any idea about that?