A problem file includes the requirements of a degree program, any predetermined parts of the schedule, as well as any additional requirements from the requirements pane. A problem file is created when you click "Save Requirements".
This is currently a known issue with our tool when using Safari, in particular with the browser's behavior when told to stretch the applet to 100% of the available space. Please try the fixed size version.
Our system uses a pruning mechanism to reduce the number of extraneous courses in a solution; in rare cases, the pruning rules we use do not have any solutions, in which case the unpruned schedule is returned. Simply regenerating another schedule with the same constraints will likely yield a smaller, pruned schedule.
This means that the requirements given to the tool cannot all be satisfied at once, which is usually an indication that the input is incorrect. For instance, it is impossible to generate a plan to satisfy the requirement "Do not schedule 6.001" as well as "6.001 AFTER Fall 2006".
A less obvious example can happen if you've populated PastSemesters by importing a grade report but also loaded in another schedule file--if the grade report and schedule fileq indicate that the same course should be taken in different semesters, then no solution can be found.