Help with array of compound type

HDF5 Library
1

I am using HDF5 in C# via HDF.PInvoke.1.10. I have an array of a compound type that I wish to add to an encompassing compound type. When I get the size of the array type to add it to the encompassing compound type, it returns what appears to be a invalid pointer location.

hsize_t[] max_dims = { H5S.UNLIMITED };
hid_t header_array = H5T.array_create(_header_kvt, 1, max_dims);
H5T.get_size(header_array);

Returns:
0xffffffffffffffe0

Thanks,
Vince