Hi Danielle,
The reason most Probably is that the Program is in a while loop and your Knob is outside the while Loop. So when the Program is run the Knob value is taken and Program enters While Loop. Now if you change the Knob this has no effect as Program is Already in the Loop with the Existing Value.
You may want to Move the Knob within the While Loop to Have its effect on the Program.
All this on my part is just guess work. It would be better if you cou8ld post the VI or Picture or Better explain what is on your diagram.
Mache
Good Luck!
Mache