Template escape url returned an empty list. at /opt/webwork/webwork2/lib/WeBWorK/Template.pm line 159.
The only other thing I see is that after running upgrade_admin_db.pl, "Upgrade courses" still says that the admin course DB is out of date. ("Database tables need updating.") Upgrading it from "Upgrade courses" doesn't change this, though it updated the DB for the regular courses just fine.
I've run check_modules.pl and pdflatex check_latex.tex, and both runs are clean.