Moodle Update 4.0 Questions - Error Reading From Database

I have recently taken over a moodle site run by our former head of department. I am taking over between us handing it over to the new head of department in a month or two. I have no experience with computers. I have attempted to update moodle to the latest update 4.0. Everything has gone okayish... The only problem I have now is that the questions in the question bank keep having an issue with reading the database. I am not sure if I have forgotten to do something with the database while updating, but I am concerned that I will not be able to access any of the questions we have built up over time. Any help with this problem would be most appreciated. Thank you for your time. *Update Here is the error message I receive when I am in debugging mode: ``` Debug info: Unknown column 'q.category' in 'on clause' SELECT q.*, qc.contextid FROM mdl6d_question q JOIN mdl6d_question_categories qc ON q.category = qc.id WHERE q.parent = ? -- line 233 of /question/type/combined/combiner/base.php: call to mysqli_native_moodle_database->get_records_sql() -- line 190 of /question/type/combined/questiontype.php: call to qtype_combined_combiner_base::get_subq_data_from_db() -- line 961 of /lib/questionlib.php: call to qtype_combined->get_question_options() -- line 1028 of /lib/questionlib.php: call to _tidy_question() -- line 930 of /lib/questionlib.php: call to get_question_options() -- line 847 of /mod/quiz/report/statistics/report.php: call to question_load_questions() -- line 83 of /question/bank/statistics/classes/helper.php: call to quiz_statistics_report->load_and_initialise_questions_for_calculations() -- line 105 of /question/bank/statistics/classes/helper.php: call to qbank_statistics\helper::load_question_stats() -- line 134 of /question/bank/statistics/classes/helper.php: call to qbank_statistics\helper::load_question_stats_item() -- line 180 of /question/bank/statistics/classes/helper.php: call to qbank_statistics\helper::calculate_average_question_stats_item() -- line 63 of /question/bank/statistics/classes/columns/discrimination_index.php: call to qbank_statistics\helper::calculate_average_question_discrimination_index() -- line 220 of /question/classes/local/bank/column_base.php: call to qbank_statistics\columns\discrimination_index->display_content() -- line 1199 of /question/classes/local/bank/view.php: call to core_question\local\bank\column_base->display() -- line 1119 of /question/classes/local/bank/view.php: call to core_question\local\bank\view->print_table_row() -- line 1095 of /question/classes/local/bank/view.php: call to core_question\local\bank\view->print_table() -- line 986 of /question/classes/local/bank/view.php: call to core_question\local\bank\view->display_questions() -- line 756 of /question/classes/local/bank/view.php: call to core_question\local\bank\view->display_question_list() -- line 60 of /question/edit.php: call to core_question\local\bank\view-&g...