From time to time I have this issue and have tried many things to correct it. Sometimes they work and sometimes they do not work. Please try the following:
1. Go to the "VIEW" menu and zoom in or out. 75% and 100% seem to be the best zoom sizes.
2. Press alt+space bar and try "Restore" if the window is maximized or try "Max" if the window is not maximized.
3. Press insert+Escape or try insert+ctl+Escape to reset the JAWS scripts.
4. If push comes to shove, I kill JAWS and restart it.
Most of the time, one of these methods will correct the problem.