I ran into a problem the other day while working on an application. Sometimes the Progressbar that monitored an event would not fill in as fast as the event completed. Thus, in order to get the progressbar to instantaneously fill, simply specify a value that is below the current value.

For example,

progressbar.Value = 100;
progressbar.Value = 99;
progressbar.Value = 100;

Will instantly fill the progressbar object to 100%. Hope this helps!