I've just been trying something to see if the problem was related to the binding. I added in another textbox on the form which was not bound to anything and set that textbox's text value during the calculation, but it does not get set up when the calculation is called from the grid's update code. It does however get set when the calculation is called from outside of the grid. The grid is in an asp updatepanel, could this have something to do with it?

If I remember correctly the updatepanel is supposed to be AJAX magic, is that right? Is there something that needs to be configured on their server to make AJAX work? Or am I going down the wrong path here?