Description of problem:
Some read enablements end up being duplicated somehow.  The result is
that multiple enablements for the same instance are active at the same
time.  Pretty much any PL/SQL that looks at enablements is going to
barf then.  A typical webalert will report "Too many enablements for
11542714"

How reproducible:
Fairly unusual.  Actually only about 3 classes have ever been affected.

Steps to Reproduce:
Not sure yet, but I suspect it involves the instructor double-clicking
the enablement confirmation.  Certainly the "default student" has had
this problem in some cases so it's probably not a student interaction.