Another version of LockDown Browser has been released for Mac, 2.1.1.05, that includes a fix for this issue. Students can either update their existing versions of LDB on their machines or find the download on this website.
Users running the latest version, 2.1.1.04, of LockDown Browser on a Mac are seeing this error: "There is a problem with the settings for this exam. Please notify your instructor that they need to access the LockDown Browser Dashboard to fix the problem" when trying to access a LockDown Browser enabled quiz when navigating to that quiz from the "Assignments" tab in the course navigation. Respondus is currently aware of the issue and working on a fix to deploy a new version of LockDown Browser for Mac that has a fix for this bug.
In the meantime, the work around for this issue is for instructors to enable the "Quizzes" or "Modules" tab in the course navigation and have the students access the exam by clicking into "Quizzes" and NOT from "Assignments". Navigating to the exam from "Quizzes" (or from the linked exam in "Modules") should bypass this error and allow students to take the exam.