Unable to recognise UI element on Internet Explorer pop up dialogue

I’m having trouble selecting an element on a pop up window in internet explorer. I’ve highlighted the situation below in the screenshot. I’m using the “Indicate Element” option in UI Explorer and have tried all the different UI Frameworks to no avail. As I hover the mouse over the desired element the highlighted box appears over a completely different element making it impossible to construct a selector for the desired element (OK button).

I’ve tried to construct the selector manually by inspecting the source HTML but this doesn’t provide the right result (the click activity simply completes without error and without having clicked the OK Button).

There are other windows within this application for which I have successfully configured element clicks but for some reason it won’t work on this particular window. It is worth mentioning that the application in question is very old and has some arcane and dated Javascript.

Any help would be greatly appreciated!