The only glitch in upgrading to 2-4 might be the necessity of installing an extra CPAN module or two. (Running bin/check_modules.pl will often provide an alert for this but it occasionally misses one -- and sometimes people forget to run it when they upgrade. )
Error messages that contain "unable to locate...." language often indicate that a CPAN module is missing.
WeBWorK Main Forum
Recovering grades
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