Here's the error message:
Can't call method "assignment_type" on an undefined value at /opt/webwork/webwork2/lib/WeBWorK/ContentGenerator/Instructor/ProblemSetDetail.pm line 1748.
The information below can help locate the source of the problem.
in WeBWorK::ContentGenerator::Instructor::ProblemSetDetail::body called at line 152 of /opt/webwork/webwork2/lib/WeBWorK/Template.pm
in WeBWorK::Template::template called at line 486 of /opt/webwork/webwork2/lib/WeBWorK/ContentGenerator.pm
in WeBWorK::ContentGenerator::content called at line 194 of /opt/webwork/webwork2/lib/WeBWorK/ContentGenerator.pm
in WeBWorK::ContentGenerator::go called at line 353 of /opt/webwork/webwork2/lib/WeBWorK.pm