Sometimes, during a long process, you may not see visible changes that you programmed, such as a change in a progress bar or status label. It seems that the code isn't being executed. The problem is that, although the code is actually being executed, it's not being shown. Access often tries to finish other code before showing something on the screen. In the case of a progress bar, the progress bar is being updated, but Access isn't going to show it until the process is complete. To get it to show the visible effects of your code, put DoEvents immediately after the code referring to the visible object.
DoEvents tells Access to wait for other processes before continuing. Any output to the screen will, thus, be executed before the code continues. DoEvents is also helpful when you need to make sure something is updated before using it.