In order to narrow down the location of the problem, it is first necessary to identify the window that was active when the error occurred. This is usually self-evident when the window is a display window, but may be less so if the window is an object window. However, an object window is activated upon receiving a message that typically originates from a display window, and therefore the problem may be effectively tracked down by beginning the search with the display window.
The first step is therefore to determine the display window with which the user was interacting when the error occurred. For documentation purposes, the window's title may be used to identify the window.
Step #1: Identify the window with which the user was interacting when the error occurred, and note its title.
Identification of the active window allows the search for the problem to be focused on the window procedure for that window. It is likely that the problem lies within that window procedure or a subroutine invoked from that window procedure. If not, the active window usually passes a message to another window which in turn causes the problem; this may be determined in the isolation phase (see Problem Isolation).