[Duke461]

So, that constraint you've been doing should be kept, it's just not the only one you want to use. all you're saying to inventor is make the point you selected in contact with the other point you selected. There are a few ways to handle this, some of them are not very good long term solutions depending on your constraints, but you'll need to do some guess and check on all of them:
1. if the top of the platform is flush with another spot, you can flush the board to that location.
2. make holes in the platform and the board, and then constrain those together.
3. using the second button on the constrain type list, angle, select the top face of the board and the top face of the platform. Before you click both faces, make sure the solution is set to Directed Angle, as opposed to the default Explicit Reference Vector. Then make sure the angle is set at 0 (that should be the default).
One of those/A Combination of those should work.
Hope this helps,
-Duke
P.S. If this did not help, please help me know, im happy to try and help more.