I've barely used labview and never used interop with it. So excuse me if I'm not a good help.
There are a couple of problems involved here.
1- By using
out double[,]
I'm guessing you want to get a memory block, reserved in the labview VI. This is a problem by it self. Memory blocks cannot be moved freely between managed and unmanaged code.
As you say you want to "send" a bi dimensional array to labview. You might want to try to leave no attribute (out nor ref) to the array parameter.
2- Parameters passed to "native" libraries are usually subjected to Marshalling, there is currently no implementation for a Marshalling a multi dimensional array, at least that I know of, I had to build my own some years ago.
I guess lab view should have definition for Custom Marshallers or you'll have to build your own:
http://msdn.microsoft.com/en-us/library/d3cxf9f0(v=VS.90).aspx[
^]
link above has been fixed, the "x" at the very end was missing. Upss!!
Give me some Labview API references and I'll give it another look.
Good luck!!