Clarified the documentation here

lang/en/help/enrolmentkey.html

@@ -9,9 +9,10 @@
 
 <P>If you put something here, then students who are trying 
    to get in for the FIRST TIME ONLY will be asked to supply 
-   this word or phrase.  (If you have also turned on 
-   guest access then guests will be challenged for the 
-   key EVERY TIME they log in).
+   this word or phrase.  The guest account can also get in
+   to the course using the enrolment key - but it will be asked
+   for the key EVERY TIME a guest logs in the course. (This occurs
+   even if you have specified 'no guests are allowed')
 
 <P>The idea is that you will supply the key to authorised 
    people using another means like private email, snail mail,

lang/en/help/guestaccess.html

@@ -12,7 +12,7 @@
    look around at your work, or to let students see a course before 
    they have decided to enrol.
 
-<P>If you also set an enrolment key (usually a good idea), 
-   then the guest user will be challenged to provide the 
-   enrolment key EVERY TIME they log in to the course.
+<P>If you have Guest access turned off, but have an enrolment key 
+   defined, then guests can still get in provided they can provide 
+   the right enrolment key.