Whenever I try to add an activity to a section I get this error:

can not find data record in database table course_modules

Debug info: SELECT id,course FROM

WHERE id = ?
[array (
0 => 3338,
)]
Error code: invalidrecord
Stack trace:
line 1403 of /lib/dml/moodle_database.php: dml_missing_record_exception thrown
line 1379 of /lib/dml/moodle_database.php: call to moodle_database->get_record_select()
line 7069 of /lib/accesslib.php: call to moodle_database->get_record()
line 112 of /course/modlib.php: call to context_module::instance()
line 270 of /course/modedit.php: call to add_moduleinfo()