I have been having a similar problem.
However, on reviewing e.item.cells(2).controls(0) in quickwatch, I discovered that it was NOT a textbox!
I checked e.item.cells(2).controls(1) and this was a textbox.
I have not created any other controls that I am aware of in this cell. But, when I tested the code with the controls(1) reference it worked.
I'm still working on the "Why"