MEX difficulty - inserting into an existing struct

I am experiencing difficulty in trying to MEX a function which inserts data into a struct. The logic / code works within MatLab but fails to compile.

The generated error is: ??? Subscripted assignment dimension mismatch (size [3 x 1] ~= size [3 x 2]).

Obviously they don't match, I am trying to grow the structs 'shift' this column right and insert (often used for FIFO)

A.test = [1;1;1]

A.test = 

1
1
1

A.test = [[2;2;2] A.test]

A.test = 
2     1
2     1
2     1

Is there a standard method for moving this procedure to MEX?

I've also tried cat and a temp variable in order to compile to no success.

Many thanks, Mark

[Mark]

Looks like the following is relevant:

How do I concatenate two MX arrays in a MEX-file that emulates the HORZCAT command of MATLAB? http://www.mathworks.com/support/solutions/en/data/1-2V66G9/index.html