I had been playing for well over an hour with no problems. I was couched and walking up to a house, when I was suddenly attacked from the rear by a silent zed. I tried to sprint, but my character would only walk. I tried to jog, but again, my character would only walk. I managed to kill the zed with an ax and then I double tapped the <CTRL> key, but there was no change. My character would only walk, whether crouched, or standing. I opened the menu to check the key bindings and as expected <Shift> and <mouse #5> were both bound to turbo and <CTRL> was bound as the walk/run toggle. I erased the bindings and then re-bound them, but my character still refused to jog, or sprint.
I shut the game down and then restarted it. Again, I erased and rebound the turbo function and then I hopped onto a server to test. Everything now works again, as expected.