@charliefik,Go to properties panel and check the simulate type property to on,Simulate type helps to click on a window in the background if it is hidden under any window.
Thanks sreekanth. I found the tickbox and read the info in the link you sent. The default (simulate type tickbox not ticked, is the slowest method but most robust (and cannot run in the background, I assume means that the workflow cannot move forward while the process is incomplete maybe this is for when you are running work in parallel, I haven’t got to that bit yet).
Anyway thanks very much for pointing me in the right direction.