Troubleshooting Guide for Error -100020

If you're seeing a score of "-100020" (that's a negative number) for one of your generated schedules, it means that the scheduling engine is working to ensure that all “Must Not” groupings are respected.

If the scheduler completed with this error code (i.e. you see the text "Did not find any solutions" in the Stage column), then this article describes the next steps you should take.  (For background, you may also want to check out Why didn't the engine find any results?.)

If the scheduler is still running (i.e. you see the text "Solving (4 of 6)" in the Stage column), and it's been stuck on this error code for a while (i.e. over an hour), you might want to take corrective action right now. There's a small chance that your caseload will still produce viable schedules before the end of its computation window, but it's not looking good. This article describes the next steps you should take.

The Easy Button

If you're in a rush and prefer not to get into the weeds, try using the following links on your caseload page:

  • Convert "Must" groupings  (by far, using this caseload transformation is the easiest way to get past this error)
  • Convert student "Must Not" entries
  • Clear delivery models
  • Remove exact time spans
  • Do all reversible transformations
  • The Nuclear Option

This is the quickest (and least-pain) way to get you a good starting point.

Reduce "Hard" Constraints

If your caseload has too many "hard" constraints, then it will severely slow down the scheduler. In fact, it may slow down so much that it will take weeks or months for the supercomputers to find a solution.  More info.

If this is happening to you, you may either:

  • Remove the "hard" constraints altogether
  • Replace the "hard" constraints with "soft" constraints.  More info.

Generally speaking, please reconsider any self-imposed constraints. Some of your constraints come from your state's laws, or from policies that your administration has put in place. If any of the constraints you've entered are really your own preferences, try removing them. The scheduler works best when the only hard constraints are the ones that are absolutely necessary.

Here are some suggestions for your caseload:

  • Consider converting any "Must Not" groupings in your caseload to “Prefer Not” groupings

The easiest way to do some of these things is to use one of the following "Caseload Transformations" on your caseload page:

  • Convert "Must" groupings  (by far, using this caseload transformation is the easiest way to get past this error)
  • Convert student "Must Not" entries
  • Clear delivery models
  • Remove exact time spans
  • Do all reversible transformations
  • The Nuclear Option

However, you can also make manual changes to your caseload to make the updates yourself.

After removing or replacing some/all of your hard constraints, try scheduling again.

Last Resort

If you have an unusually large caseload, or relatively few days to see all of your students, the scheduling engine may not have enough available therapy time to squeeze everything in.  More info.

Before applying the last resort, you should first try the above suggestions:

  • Resolve all of your conflicting constraints
  • Remove/replace all of your "hard" constraints

If you've already done these things, and are still having trouble, please follow the generic instructions here under "Caseload Is Too Large".

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