Hi Ocean,
Try like below code-
Delay(...Specify time........)
Set popupB = Sys.Process("iexplore", 2).FindChild("wndCaption","OK",100)
IF popupB.Exists then
popupB.click
else
log.Message("Pop up B not yet Visible")
End If
In this code first of all I am waiting some time (TC may need some time for synch)hence I am waiting and then searching specific caption from pop-up B like (OK).
When I have found OK it will be click on it and go for next.
It will be happen just because our Application and TC time execution not synched.