Checkbox within swftable gets ticked by UFT but does not save to database


I have a regression script which has been working for years but in the past few weeks my script now fails. This is because the ticks to the boxes in my software by UFT set by .setcelldata do not seem to be registering correctly with the application. Weirdly, the ticks show on the screen when UFT selects them but there are also counts on screen which should update after every click but the click doesnt seem to register. On saving the on screen form after UFT has ticked the checkboxes, then the ticks are not saved to the database either.... When i use the mouse in the application it works as expected but its just when UFT ticks the checkboxes that the problem occurs. The code is below:

intGridRowCount = SwfWindow("Control").SwfWindow("Letting Breaks").SwfTable("dgSubletPackages").RowCount

= 0

Do Until i = intGridRowCount - 1
    i = i 1
    blnCapReached = SwfWindow("Control").SwfWindow("Letting Breaks").SwfTable("dgSubletPackages").GetCellData(i, "Cap Reached")
        IF blnCapReached = 0 THEN 
         SwfWindow("Control").SwfWindow("Letting Breaks").SwfTable("dgSubletPackages").SetCellData i,"Let",True
        End if 


I have also tried using .ActiveCell which DOES work as per using the mouse BUT after clicking about 10 checkboxes then UFT crashes on me, so i cant use that function. I have also spoke to the developer of the application who has assured me there have been no changes to the objects in the application in the latest release i a currently testing on.

Any ideas would be great.