Can you clear the keyboard buffer?

We have some systems training exercises where the users interact using the keyboard and some Function keys.  The first time through on a published file, everything works as expected.  When re-entering the file(s), the exercise will freeze up at different slides each time.  I'm not sure, but it acts like there is some issue with the keyboard buffer.  Is there any way to clear out everything upon entering the first slide?

We ensured the Preferences did not show any keyboard conflicts, nor are we using anything that Windows would conflict with.  We tested on several computers with the same result.